staging: wfx: drop protection for asynchronous join during scan

In former code (before the inclusion of the driver in mainline kernel),
hif_join() could run asynchronously. When a join request was in
progress, it was forbidden to launch hif_scan().

Now, hif_join() is always run synchronously. There is no more reasons to
keep a protection against this case.
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200420160311.57323-13-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/scan.c

@@ -110,9 +110,6 @@ int wfx_hw_scan(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
 	if (vif->type == NL80211_IFTYPE_AP)
 		return -EOPNOTSUPP;
 
-	if (wvif->state == WFX_STATE_PRE_STA)
-		return -EBUSY;
-
 	wvif->scan_req = hw_req;
 	schedule_work(&wvif->scan_work);
 	return 0;