MAINTAINERS: brcmnand: Add Broadcom internal mailing-list

The Broadcom NAND driver is used by many different groups at Broadcom
now, so use the same mailing-list we use for other areas of the kernel.

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