i965/fs: Fix lower_load_payload() to take into account non-zero reg_offset.
i965/fs: Fix lower_load_payload() to take into account non-zero reg_offset.

Fixes metadata guess when instructions in the program specify a
destination register with non-zero reg_offset and when the payload of
a LOAD_PAYLOAD spans several registers.

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

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler