MAINTAINERS: Update NXP FEC maintainer

Emails to Joakim Zhang bounce, update the list of maintainers per
feedback from Clark Wang and designate Wei Fang as the primary
maintainer.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>