mtd: rawnand: remove misguided comment of nand_get_device()

After commit 8cba3234 ("mtd: rawnand: protect access to rawnand devices
while in suspend"), it will wait while in suspend rather than returning
errors. So remove the misguided comment about return value.

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220819021846.2924539-1-chenxiaosong2@huawei.com