MAINTAINERS: wifi: update Jeff Johnson e-mail address

I now have a @kernel.org e-mail address, so use that for my
maintenance activities.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240217-update-maintainer-v1-1-1426cf7a8bb1@quicinc.com