mtd: onenand: samsung: return an error if 'mtd_device_parse_register()' fails

If 'mtd_device_parse_register()' fails, we still return 0 which mean
success.
Return the error code instead, as done in all the other error handling
paths.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>