r300/compiler: Move declaration before code.

r300/compiler: Move declaration before code.

Fixes these GCC warnings on linux-x86 build.
radeon_program_alu.c: In function ‘r300_transform_trig_simple’:
radeon_program_alu.c:882: warning: ISO C90 forbids mixed declarations and code
radeon_program_alu.c:932: warning: ISO C90 forbids mixed declarations and code
radeon_program_alu.c: In function ‘radeonTransformTrigScale’:
radeon_program_alu.c:996: warning: ISO C90 forbids mixed declarations and code
radeon_program_alu.c: In function ‘r300_transform_trig_scale_vertex’:
radeon_program_alu.c:1033: warning: ISO C90 forbids mixed declarations and code