MAINTAINERS: assign em_canid.c additionally to CAN maintainers

MAINTAINERS: assign em_canid.c additionally to CAN maintainers

The extended match rule em_canid is used to classify CAN frames based
on their CAN Identifier. To keep the CAN maintainers in the loop for
relevant changes which might affect the CAN specific functionality add
em_canid.c to the CAN NETWORK LAYER files.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20241219190837.3087-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>