drm/xe/guc: s/xe_guc_send_mmio/xe_guc_mmio_send

Now aligns with the xe_guc_ct_send naming.

Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Philippe Lecluse <philippe.lecluse1@gmail.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>