mtd: rawnand: mtk: Factorize out the logic cleaning mtk chips

There are some un-freed resources in one of the error path which would
benefit from a helper going through all the registered mtk chips one by
one and perform all the necessary cleanup. This is precisely what the
remove path does, so let's extract the logic in a helper.

There is no functional change.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Matthias Brugger <matthias.bgg@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20240826153019.67106-1-miquel.raynal@bootlin.com