mtd: rawnand: davinci: Rewrite function description

The original comment that describes the function
nand_davinci_read_page_hwecc_oob_first() is very obscure and it is hard
to understand what it is for.

Cc: <stable@vger.kernel.org> # v5.2
Fixes: a0ac778e

 ("mtd: rawnand: ingenic: Add support for the JZ4740")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20211016132228.40254-3-paul@crapouillou.net