cfg80211: fix -Wcast-qual warnings

When enabling -Wcast-qual e.g. via W=3, we get a lot of
warnings from this file, whenever it's included. Since
the fixes are simple, just do that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20220202104617.6a1d52213019.I92d82e7251cf712faa43fd09db3142327a3bce3d@changeid


Signed-off-by: Johannes Berg <johannes.berg@intel.com>