MAINTAINERS: list PTP drivers under networking

PTP patches go via the netdev trees, add drivers/ptp/ to the networking
entry so that get_maintainer.pl --scm lists those trees above Linus's
tree.

Thanks to the real entry using drivers/ptp/* the original entry will
still be considered more specific / higher prio.

Acked-by: Richard Cochran <richardcochran@gmail.com>
Link: https://patch.msgid.link/20241130214100.125325-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>