i965: Fix an unused variable warning in the release build.
i965: Fix an unused variable warning in the release build.

It's used in an assert, but we have this as a member of the class anyway.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,wolf96/glsl-optimizer,mapbox/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,metora/MesaGLSLCompiler,zz85/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,wolf96/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,mcanthony/glsl-optimizer,mcanthony/glsl-optimizer,dellis1972/glsl-optimizer,dellis1972/glsl-optimizer,metora/MesaGLSLCompiler,wolf96/glsl-optimizer,metora/MesaGLSLCompiler,mapbox/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,benaadams/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,mapbox/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,dellis1972/glsl-optimizer,zeux/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,zeux/glsl-optimizer,djreep81/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,tokyovigilante/glsl-optimizer