cfg80211: reg: Init wiphy_idx in regulatory_hint_core()

Core regulatory hints didn't set wiphy_idx to WIPHY_IDX_INVALID. Since
the regulatory request is zeroed, wiphy_idx was always implicitly set to
0. This resulted in updating only phy #0.
Fix that.

Fixes: 806a9e39 ("cfg80211: make regulatory_request use wiphy_idx instead of wiphy")
Signed-off-by: Andrei Otcheretianski <andrei.otcheretianski@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
[add fixes tag]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>