libertas: fix use-before-check violation

According to Coverity (kudo's to Adrian Bunk), we had one use-before-check
bug in libe libertas driver. This patch fixes this issue.
Signed-off-by: NHolger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/libertas/scan.c

@@ -298,7 +298,8 @@ static int lbs_do_scan(struct lbs_private *priv, uint8_t bsstype,
 	uint8_t *tlv;	/* pointer into our current, growing TLV storage area */
 
 	lbs_deb_enter_args(LBS_DEB_SCAN, "bsstype %d, chanlist[].chan %d, chan_count %d",
-			   bsstype, chan_list[0].channumber, chan_count);
+		bsstype, chan_list ? chan_list[0].channumber : -1,
+		chan_count);
 
 	/* create the fixed part for scan command */
 	scan_cmd = kzalloc(MAX_SCAN_CFG_ALLOC, GFP_KERNEL);