MAINTAINERS: switch to different email address

Switching to private mail account as work email is polluted with a legal
disclaimer. Just making it extra clear by changing the email address in
the MAINTAINERS file as well.

Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Arend van Spriel <aspriel@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201220141807.17278-1-aspriel@gmail.com