mtd: sm_ftl: Fix typos in comments

Fix typo in the description of the 'succesfull'.

Signed-off-by: Bo Liu <liubo03@inspur.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230621020331.1508-1-wangdeming@inspur.com