r300/compiler: Move declaration before code.

r300/compiler: Move declaration before code.

Fixes these GCC warnings on linux-x86 build.
r300_fragprog_emit.c: In function ‘emit_alu’:
r300_fragprog_emit.c:143: warning: ISO C90 forbids mixed declarations and code
r300_fragprog_emit.c:156: warning: ISO C90 forbids mixed declarations and code
r300_fragprog_emit.c: In function ‘finish_node’:
r300_fragprog_emit.c:271: warning: ISO C90 forbids mixed declarations and code
r300_fragprog_emit.c: In function ‘emit_tex’:
r300_fragprog_emit.c:344: warning: ISO C90 forbids mixed declarations and code