Merge tag 'mtd/core-fixes-before-nvmem-layouts-for-6.4' into mtd/next

Core MTD changes:
* Prepare mtd_otp_nvmem_add() to handle -EPROBE_DEFER
* Fix error path for nvmem provider
* Fix nvmem error reporting
* Provide unique name for nvmem device

These changes are expected to be pulled before applying nvmem layouts
support in order to get a fully working support in all situations.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>