mtd: nand: mediatek: return error code of nand_scan_ident/tail() on error

The nand_scan_ident/tail() returns an appropriate error value when
it fails.  Use it instead of the fixed error code -ENODEV.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>