p54: potential signedness issue in p54_parse_rssical()

"entries" is unsigned here, so it is never less than zero.  In theory,
len could be less than offset so I have added a check for that.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/p54/eeprom.c

@@ -541,8 +541,9 @@ static int p54_parse_rssical(struct ieee80211_hw *dev,
 		entries = (len - offset) /
 			sizeof(struct pda_rssi_cal_ext_entry);
 
-		if ((len - offset) % sizeof(struct pda_rssi_cal_ext_entry) ||
-		    entries <= 0) {
+		if (len < offset ||
+		    (len - offset) % sizeof(struct pda_rssi_cal_ext_entry) ||
+		    entries == 0) {
 			wiphy_err(dev->wiphy, "invalid rssi database.\n");
 			goto err_data;
 		}