intel/fs: fix a couple of descriptor mistakes

intel/fs: fix a couple of descriptor mistakes

I found those issues while testing DOOM eternal and Ian also ran into
it with other shaders.

We write the desc register in SIMD1 exec_all, so all the data is in
the first component. We need to make sure to pass that component in
the lower SEND instructions.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23354>