scsi: hisi_sas: Remove stray fallthrough annotation

This case statement doesn't fall through any more so remove the fallthrough
annotation.

Link: https://lore.kernel.org/r/20220317075214.GC25237@kili


Acked-by: John Garry <john.garry@huawei.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>