mtd: Fix a typo in a comment

o and t are swapped.
s/mtdpsotre/mtdpstore/

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/de1b1134f056ea7563bb0a9bb2f66ede1475728d.1659816434.git.christophe.jaillet@wanadoo.fr