scsi: fas216: Fix fall-through warning for Clang

Fix the following fallthrough warning (on ARM):

drivers/scsi/arm/fas216.c:1379:2: warning: unannotated fall-through between switch labels [-Wimplicit-fallthrough]
           default:
           ^
   drivers/scsi/arm/fas216.c:1379:2: note: insert 'break;' to avoid fall-through
           default:
           ^
           break;
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/lkml/202107260355.bF00i5bi-lkp@intel.com/Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

drivers/scsi/arm/fas216.c

@@ -1375,6 +1375,7 @@ static void fas216_busservice_intr(FAS216_Info *info, unsigned int stat, unsigne
 		case IS_COMPLETE:
 			break;
 		}
+		break;
 
 	default:
 		break;