mtd: parsers: refer to ARCH_BCMBCA instead of ARCH_BCM4908

mtd: parsers: refer to ARCH_BCMBCA instead of ARCH_BCM4908

Commit dd5c672d7ca9 ("arm64: bcmbca: Merge ARCH_BCM4908 to ARCH_BCMBCA")
removes config ARCH_BCM4908 as config ARCH_BCMBCA has the same intent.

Probably due to concurrent development, commit 002181f5b150 ("mtd: parsers:
add Broadcom's U-Boot parser") introduces 'Broadcom's U-Boot partition
parser' that depends on ARCH_BCM4908, but this use was not visible during
the config refactoring from the commit above. Hence, these two changes
create a reference to a non-existing config symbol.

Adjust the MTD_BRCM_U_BOOT definition to refer to ARCH_BCMBCA instead of
ARCH_BCM4908 to remove the reference to the non-existing config symbol
ARCH_BCM4908.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221116124932.4748-1-lukas.bulwahn@gmail.com