r300/compiler: Move declaration before code.

r300/compiler: Move declaration before code.

Fixes these GCC warnings on linux-x86 build.
radeon_pair_schedule.c: In function ‘emit_all_tex’:
radeon_pair_schedule.c:244: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c: In function ‘destructive_merge_instructions’:
radeon_pair_schedule.c:291: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c:438: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c: In function ‘scan_read’:
radeon_pair_schedule.c:619: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c: In function ‘scan_write’:
radeon_pair_schedule.c:645: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c: In function ‘schedule_block’:
radeon_pair_schedule.c:673: warning: ISO C90 forbids mixed declarations and code
radeon_pair_schedule.c: In function ‘rc_pair_schedule’:
radeon_pair_schedule.c:730: warning: ISO C90 forbids mixed declarations and code