dmaengine: consistently return string literal from switch-case

There is no need to have 'break;' statement in the default case followed by
return certain string literal when all other cases have returned the string
literals. So, refactor it accordingly.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20200226101842.29426-4-andriy.shevchenko@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

include/linux/dmaengine.h

@@ -1560,9 +1560,7 @@ dmaengine_get_direction_text(enum dma_transfer_direction dir)
 	case DMA_DEV_TO_DEV:
 		return "DEV_TO_DEV";
 	default:
-		break;
+		return "invalid";
 	}
-
-	return "invalid";
 }
 #endif /* DMAENGINE_H */