wilc1000: fix crash observed in AP mode with cfg80211_register_netdevice()

Monitor(mon.) interface is used for handling the AP mode and 'ieee80211_ptr'
reference is not getting set for it. Like earlier implementation,
use register_netdevice() instead of cfg80211_register_netdevice() which
expects valid 'ieee80211_ptr' reference to avoid the possible crash.

Fixes: 2fe8ef10 ("cfg80211: change netdev registration/unregistration semantics")
Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220504161924.2146601-3-ajay.kathat@microchip.com