mtd: parsers: bcm47xxpart: make read-only array possible_nvram_sizes static const

Don't populate the read-only array possible_nvram_sizes on the stack at
run time, instead make it static const.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240822164632.638171-1-colin.i.king@gmail.com