mtd: core: prepare mtd_otp_nvmem_add() to handle -EPROBE_DEFER

NVMEM soon will get the ability for nvmem layouts and these might
not be ready when nvmem_register() is called and thus it might
return -EPROBE_DEFER. Don't print the error message in this case.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230308082021.870459-4-michael@walle.cc