i915: Fix GCC unused-variable warning in release build.
i915: Fix GCC unused-variable warning in release build.

i915_debug_fp.c: In function ‘i915_disassemble_program’:
i915_debug_fp.c:302:11: warning: unused variable ‘size’ [-Wunused-variable]
    GLuint size = program[0] & 0x1ff;
           ^

Signed-off-by: Vinson Lee <25a259f709b0f1b620605d2518271a846d8826e5@freedesktop.org>
Reviewed-by: Timothy Arceri <7f85c8176b2576ffafd04ac63cd29ed35ff86cb6@yahoo.com.au>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler