iwlwifi: warn when send tx power settings during scan

Add WARN_ONCE when scanning is pending. Use STATUS_SCAN_HW bit since we
can have scan canceled or completed but STATUS_SCANNING bit still set.

v1 -> v2: replace EIO to EAGAIN

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-3945.c b/drivers/net/wireless/iwlwifi/iwl-3945.c
index 176e525..4d7130c 100644
--- a/drivers/net/wireless/iwlwifi/iwl-3945.c
+++ b/drivers/net/wireless/iwlwifi/iwl-3945.c
@@ -1451,6 +1451,10 @@
 	};
 	u16 chan;
 
+	if (WARN_ONCE(test_bit(STATUS_SCAN_HW, &priv->status),
+		      "TX Power requested while scanning!\n"))
+		return -EAGAIN;
+
 	chan = le16_to_cpu(priv->contexts[IWL_RXON_CTX_BSS].active.channel);
 
 	txpower.band = (priv->band == IEEE80211_BAND_5GHZ) ? 0 : 1;