intel/fs/validate: Assert SEND [extended] descriptors are uniform

This is required by code-gen since it generates a 1-wide OR and it'll
blow up if the register width > 1.  It's also way better than the "your
register is the wrong size" assert you get from the more generic
validation check.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21094>

src/intel/compiler/brw_lower_logical_sends.cpp

@@ -370,6 +370,7 @@ lower_fb_write_logical_send(const fs_builder &bld, fs_inst *inst,
          desc = ubld.vgrf(BRW_REGISTER_TYPE_UD);
          ubld.AND(desc, dynamic_msaa_flags(prog_data),
                   brw_imm_ud(BRW_WM_MSAA_FLAG_COARSE_DISPATCH));
+         desc = component(desc, 0);
       }
 
       uint32_t ex_desc = 0;