cfg80211: remove wiphy_idx_valid

This is pretty much useless since get_wiphy_idx()
always returns true since it's always called with
a valid wiphy pointer.

Acked-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --cc net/wireless/core.c
Simple merge

diff --cc net/wireless/core.h
Simple merge

diff --cc net/wireless/nl80211.c
Simple merge

diff --cc net/wireless/reg.c
Simple merge