efi: Add missing break to dp_fill()

While this doesn't really affect anything in practice, it is better to
deal with an incorrect use of this function (calling it with a UCLASS
which is not enabled).

Add a break after the UCLASS_BLK case, to help this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Fixes: a48a8929de ("efi: Move most of efi_device_path into lib/efi")

lib/efi/device_path.c

@@ -529,6 +529,7 @@ __maybe_unused static void *dp_fill(void *buf, struct udevice *dev)
 
 			return &dp[1];
 		}
+		break;
 	}
 	case UCLASS_MMC:
 	if (IS_ENABLED(CONFIG_MMC)) {