mtd: rawnand: sm_common: drop unexpected word 'is' in the comments

there is an unexpected word 'is' in the comments that need to be dropped

file: drivers/mtd/nand/raw/sm_common.c
line: 55

/* NOTE: This layout is is not compatabable with SmartMedia, */

changed to:

/* NOTE: This layout is not compatabable with SmartMedia, */

Signed-off-by: Jiang Jian <jiangjian@cdjrlc.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220622160511.11679-1-jiangjian@cdjrlc.com