scsi: ufs: add fall through annotation

Add /* fallthrough */ annotation, to eliminate compilation warning:
warning: this statement may fall through [-Wimplicit-fallthrough=]

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Avri Altman <avri.altman@wdc.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>