mtd: parsers: ofpart: make symbol 'bcm4908_partitions_quirks' static

The sparse tool complains as follows:

drivers/mtd/parsers/ofpart_core.c:25:32: warning:
 symbol 'bcm4908_partitions_quirks' was not declared. Should it be static?

This symbol is not used outside of ofpart_core.c, so this
commit marks it static.

Fixes: 457da931b608 ("mtd: parsers: ofpart: support BCM4908 fixed partitions")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210304064600.3279138-1-weiyongjun1@huawei.com