MAINTAINERS: brcmnand: Add co-maintainer for Broadcom SoCs

Adding myself as co-maintainer of nand controller driver
for the Broadcom SoCs.

Signed-off-by: Kamal Dasu <kdasu.kdev@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>