r300/compiler: Move declaration before code.

r300/compiler: Move declaration before code.

Fixes these GCC warnings with linux-x86 build.
radeon_emulate_branches.c: In function ‘handle_if’:
radeon_emulate_branches.c:65: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c:71: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c: In function ‘handle_else’:
radeon_emulate_branches.c:94: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c: In function ‘handle_endif’:
radeon_emulate_branches.c:201: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c: In function ‘fix_output_writes’:
radeon_emulate_branches.c:267: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c:284: warning: ISO C90 forbids mixed declarations and code
radeon_emulate_branches.c: In function ‘rc_emulate_branches’:
radeon_emulate_branches.c:307: warning: ISO C90 forbids mixed declarations and code