Some functions should never have been exported (the ones prefixed by
__*), in this case simply drop the documentation, we never want
anybody to use this function from the outside.

For the other functions, enhance the style.
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200929230124.31491-14-miquel.raynal@bootlin.com