MAINTAINERS: Add BCM4908 maintainer to BCMBCA entry

Since BCM4908 SoC support is merged into ARCH_BCMBCA, add BCM4908
maintainer Rafal to bcmbca maintainer list.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20220803175455.47638-9-william.zhang@broadcom.com


Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>