staging: mt7621-mmc: Add annotations about held locks

The functions msdc_command_resp and msdc_do_request are always called
with the host->lock lock held. By adding annotations, sparse is
informed about that.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Reviewed-by: NeilBrown <neil@brown.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>