mtd: ubi: Put MTD device after it is not used

mtd: 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>
Upstream Linux commit: b95f83ab762dd6211351b9140f99f43644076ca8

Signed-off-by: Alexander Vickberg <wickbergster@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>