scsi: megaraid_sas_fusion: Mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where
we are expecting to fall through.

Notice that, in this particular case, I replaced "Fall thru" with a "Fall
through" annotation and added a dash as a token in order to separate the
"Fall through" annotation from the rest of the comment on the same line,
which is what GCC is expecting to find.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/megaraid/megaraid_sas_fusion.c

@@ -3453,7 +3453,7 @@ complete_cmd_fusion(struct megasas_instance *instance, u32 MSIxIndex)
 				atomic_dec(&lbinfo->scsi_pending_cmds[cmd_fusion->pd_r1_lb]);
 				cmd_fusion->scmd->SCp.Status &= ~MEGASAS_LOAD_BALANCE_FLAG;
 			}
-			//Fall thru and complete IO
+			/* Fall through - and complete IO */
 		case MEGASAS_MPI2_FUNCTION_LD_IO_REQUEST: /* LD-IO Path */
 			atomic_dec(&instance->fw_outstanding);
 			if (cmd_fusion->r1_alt_dev_handle == MR_DEVHANDLE_INVALID) {