cmd: ubifs: Move ubifs_initialized checking into cmd_ubifs_umount()

cmd_ubifs_umount() function would be called directly instead of involving
whole command machinery in generic firmware loader, so checking on
ubifs_initialized status need to be done in cmd_ubifs_umount() without
breaking original functionality design.

Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>
[trini: Fix conflicting type error in cmd/ubi.c]
Signed-off-by: Tom Rini <trini@konsulko.com>

cmd/ubi.c

@@ -47,8 +47,7 @@ struct selected_dev {
 static struct selected_dev ubi_dev;
 
 #ifdef CONFIG_CMD_UBIFS
-int ubifs_is_mounted(void);
-void cmd_ubifs_umount(void);
+#include <ubifs_uboot.h>
 #endif
 
 static void display_volume_info(struct ubi_device *ubi)