MAINTAINERS: wifi: cw1200: add net-cw1200.h

MAINTAINERS: wifi: cw1200: add net-cw1200.h

This is part of an effort [1] to assign a section in MAINTAINERS to header
files that relate to Networking. In this case the files with "net" in
their name.

[1] https://lore.kernel.org/netdev/20240821-net-mnt-v2-0-59a5af38e69d@kernel.org/

It seems that net-cw1200.h is part of the CW1200 WLAN driver and
this it is appropriate to add it to the section for that driver.

Signed-off-by: Simon Horman <horms@kernel.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240902-wifi-mnt-v2-1-f5ad1f36e993@kernel.org