i965/fs: Don't overwrite fs_visitor::uniforms and ::param_size during the SIMD16...

i965/fs: Don't overwrite fs_visitor::uniforms and ::param_size during the SIMD16 run.

Image variables need to allocate additional uniform slots over
nir_shader::num_uniforms.  nir_setup_uniforms() overwrites the values
imported from the SIMD8 visitor and then exits early before entering
the nir_shader::uniforms loop, so image uniforms are never re-created.
Instead leave the imported values alone, they *must* be the same for
the uniform layout of both runs to be compatible.

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