staging: greybus: MAINTAINERS: add greybus protocol drivers maintainers

Add bod to some Greybus protocol drivers maintainers, loopback and
timesync.

Signed-off-by: Bryan O'Donoghue <pure.logic@nexus-software.ie>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>