cfg80211: check wiphy driver existence for drvinfo report

cfg80211: check wiphy driver existence for drvinfo report

[ Upstream commit bfb7bac3a8f47100ebe7961bd14e924c96e21ca7 ]

When preparing ethtool drvinfo, check if wiphy driver is defined
before dereferencing it. Driver may not exist, e.g. if wiphy is
attached to a virtual platform device.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Link: https://lore.kernel.org/r/20200203105644.28875-1-sergey.matyukevich.os@quantenna.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>