wifi: mwifiex: add missing locking for cfg80211 calls

cfg80211_rx_assoc_resp() and cfg80211_rx_mlme_mgmt() need to be called
with the wiphy locked, so lock it before calling these functions.

Fixes: 36995892 ("wifi: mwifiex: add host mlme for client mode")
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240918-mwifiex-cleanup-1-v2-1-2d0597187d3c@pengutronix.de