xilinx: zynqmp: Handle fallthrough statement properly

Now intentional fallthrough in switch-case should be labelled that's why
convert comment.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>
Link: https://lore.kernel.org/r/b3e976bd3b9bbe7061fec5ba0a3b4e78fdd78394.1634556602.git.michal.simek@xilinx.com
diff --git a/board/xilinx/zynqmp/zynqmp.c b/board/xilinx/zynqmp/zynqmp.c
index b24db53..e8ae549 100644
--- a/board/xilinx/zynqmp/zynqmp.c
+++ b/board/xilinx/zynqmp/zynqmp.c
@@ -710,7 +710,7 @@
 		break;
 	case SD1_LSHFT_MODE:
 		puts("LVL_SHFT_");
-		/* fall through */
+		fallthrough;
 	case SD_MODE1:
 		puts("SD_MODE1\n");
 		if (uclass_get_device_by_name(UCLASS_MMC,