scsi: mpi3mr: Fix fall-through warning for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix a
fall-through warning by explicitly adding a break statement instead of just
letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Link: https://lore.kernel.org/r/20210604023530.GA180997@embeddedorReviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpi3mr/mpi3mr_os.c

@@ -1732,6 +1732,7 @@ static void mpi3mr_sastopochg_evt_th(struct mpi3mr_ioc *mrioc,
 				atomic_dec_if_positive
 				    (&scsi_tgt_priv_data->block_io);
 			}
+			break;
 		case MPI3_EVENT_SAS_TOPO_PHY_RC_PHY_CHANGED:
 		default:
 			break;