mtd: rawnand: omap: Various style fixes

Fix the comments style, declare the variables in a reverse Christmas
tree order, add an upper case character at the beginning of a sentence.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210610134906.3503303-5-miquel.raynal@bootlin.com