iwlegacy: propagate error return value

propogate the return value from iwl4965_get_tx_atten_grp instead
of implicitly returning -EINVAL in the error case.
Signed-off-by: NGreg Dietsche <Gregory.Dietsche@cuw.edu>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlegacy/iwl-4965.c

@@ -915,7 +915,7 @@ static int iwl4965_fill_txpower_tbl(struct iwl_priv *priv, u8 band, u16 channel,
 	if (txatten_grp < 0) {
 		IWL_ERR(priv, "Can't find txatten group for channel %d.\n",
 			  channel);
-		return -EINVAL;
+		return txatten_grp;
 	}
 
 	IWL_DEBUG_TXPOWER(priv, "channel %d belongs to txatten group %d\n",