cmd: ubifs: Do not show usage when command fails

Return value -1 cause U-Boot to print usage message. Return value
1 (CMD_RET_FAILURE) indicates failure. So fix return value when ubifs
command starts it execution and fails.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
diff --git a/cmd/ubifs.c b/cmd/ubifs.c
index 7a620c5..6a01d09 100644
--- a/cmd/ubifs.c
+++ b/cmd/ubifs.c
@@ -33,7 +33,7 @@
 
 	ret = uboot_ubifs_mount(vol_name);
 	if (ret)
-		return -1;
+		return CMD_RET_FAILURE;
 
 	ubifs_mounted = 1;
 
@@ -62,7 +62,7 @@
 {
 	if (ubifs_initialized == 0) {
 		printf("No UBIFS volume mounted!\n");
-		return -1;
+		return CMD_RET_FAILURE;
 	}
 
 	uboot_ubifs_umount();
@@ -89,7 +89,7 @@
 
 	if (!ubifs_mounted) {
 		printf("UBIFS not mounted, use ubifsmount to mount volume first!\n");
-		return -1;
+		return CMD_RET_FAILURE;
 	}
 
 	if (argc == 2)
@@ -116,7 +116,7 @@
 
 	if (!ubifs_mounted) {
 		printf("UBIFS not mounted, use ubifs mount to mount volume first!\n");
-		return -1;
+		return CMD_RET_FAILURE;
 	}
 
 	if (argc < 3)