mesa: Move declarations before code.

mesa: Move declarations before code.

This patch fixes these MSVC build errors.

  Compiling src\mesa\drivers\common\meta_blit.c ...
meta_blit.c
src\mesa\drivers\common\meta_blit.c(255) : error C2143: syntax error : missing ';' before 'type'
src\mesa\drivers\common\meta_blit.c(255) : error C2143: syntax error : missing ')' before 'type'
src\mesa\drivers\common\meta_blit.c(255) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(255) : warning C4552: '<' : operator has no effect; expected operator with side-effect
src\mesa\drivers\common\meta_blit.c(255) : error C2059: syntax error : ')'
src\mesa\drivers\common\meta_blit.c(255) : error C2143: syntax error : missing ';' before '{'
src\mesa\drivers\common\meta_blit.c(258) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(263) : error C2143: syntax error : missing ';' before 'type'
src\mesa\drivers\common\meta_blit.c(263) : error C2143: syntax error : missing ')' before 'type'
src\mesa\drivers\common\meta_blit.c(263) : error C2065: 'step' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(263) : warning C4552: '<=' : operator has no effect; expected operator with side-effect
src\mesa\drivers\common\meta_blit.c(263) : error C2059: syntax error : ')'
src\mesa\drivers\common\meta_blit.c(263) : error C2143: syntax error : missing ';' before '{'
src\mesa\drivers\common\meta_blit.c(264) : error C2143: syntax error : missing ';' before 'type'
src\mesa\drivers\common\meta_blit.c(264) : error C2143: syntax error : missing ')' before 'type'
src\mesa\drivers\common\meta_blit.c(264) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(264) : warning C4552: '<' : operator has no effect; expected operator with side-effect
src\mesa\drivers\common\meta_blit.c(264) : error C2059: syntax error : ')'
src\mesa\drivers\common\meta_blit.c(264) : error C2065: 'step' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(264) : error C2143: syntax error : missing ';' before '{'
src\mesa\drivers\common\meta_blit.c(268) : error C2065: 'step' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(268) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(269) : error C2065: 'step' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(269) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(270) : error C2065: 'step' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(270) : error C2065: 'i' : undeclared identifier
src\mesa\drivers\common\meta_blit.c(559) : warning C4244: 'function' : conversion from 'const GLint' to 'GLfloat', possible loss of data
src\mesa\drivers\common\meta_blit.c(723) : warning C4244: 'function' : conversion from 'const GLint' to 'GLfloat', possible loss of data
src\mesa\drivers\common\meta_blit.c(773) : warning C4244: 'function' : conversion from 'const GLint' to 'GLfloat', possible loss of data

Signed-off-by: Vinson Lee <vlee@freedesktop.org>