mac80211: fix ibss joining

Recent commit "mac80211: fix logic error ibss merge bssid check" fixed
joining of ibss cell when static bssid is provided. In this case
ifibss->bssid is set before the cell is joined and comparing that address
to a bss should thus always succeed. Unfortunately this change broke the
other case of joining a ibss cell without providing a static bssid where
the value of ifibss->bssid is not set before the cell is joined.

Since ifibss->bssid may be set before or after joining the cell we do not
learn anything by comparing it to a known bss. Remove this check.

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>