ubi: Put MTD device after it is not used

The MTD device reference is dropped via put_mtd_device, however its
field ->index is read and passed to ubi_msg. To fix this, the patch
moves the reference dropping after calling ubi_msg.
Signed-off-by: Pan Bian <bianpan2016@163.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

drivers/mtd/ubi/build.c

@@ -1101,10 +1101,10 @@ int ubi_detach_mtd_dev(int ubi_num, int anyway)
 	ubi_wl_close(ubi);
 	ubi_free_internal_volumes(ubi);
 	vfree(ubi->vtbl);
-	put_mtd_device(ubi->mtd);
 	vfree(ubi->peb_buf);
 	vfree(ubi->fm_buf);
 	ubi_msg(ubi, "mtd%d is detached", ubi->mtd->index);
+	put_mtd_device(ubi->mtd);
 	put_device(&ubi->dev);
 	return 0;
 }