i965/fs: Don't offset uniform registers in half().
i965/fs: Don't offset uniform registers in half().

Half gives you the second half of a SIMD16 register, but if the register
is a uniform it would incorrectly give you the next register.

Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler