mtd: rawnand: Stop passing mtd_info objects to internal functions

After having reworked the rawnand API to avoid passing mtd_info
objects around, let's do the same for internal functions.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Tested-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>