Fixes the following sparse warnings:

drivers/mtd/parsers/sharpslpart.c:222:6: warning:
 symbol 'sharpsl_nand_cleanup_ftl' was not declared. Should it be static?
Signed-off-by: NWei Yongjun <weiyongjun1@huawei.com>
Acked-by: NAndrea Adami <andrea.adami@gmail.com>
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>