staging: wfx: improve robustness of wfx_get_hw_rate()

Smatch complains:

    data_tx.c:37 wfx_get_hw_rate() warn: constraint '(struct ieee80211_supported_band)->bitrates' overflow 'band->bitrates' 0 <= abs_rl '0-127' user_rl '' required = '(struct ieee80211_supported_band)->n_bitrates'
    23          struct ieee80211_supported_band *band;
    24
    25          if (rate->idx < 0)
    26                  return -1;
    27          if (rate->flags & IEEE80211_TX_RC_MCS) {
    28                  if (rate->idx > 7) {
    29                          WARN(1, "wrong rate->idx value: %d", rate->idx);
    30                          return -1;
    31                  }
    32                  return rate->idx + 14;
    33          }
    34          // WFx only support 2GHz, else band information should be retrieved
    35          // from ieee80211_tx_info
    36          band = wdev->hw->wiphy->bands[NL80211_BAND_2GHZ];
    37          return band->bitrates[rate->idx].hw_value;

Add a simple check to make Smatch happy.

Reported-by: Dan Carpenter <[email protected]>
Signed-off-by: Jérôme Pouiller <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: jerome-pouiller

drivers/staging/wfx/data_tx.c

@@ -31,6 +31,10 @@ static int wfx_get_hw_rate(struct wfx_dev *wdev,
 		}
 		return rate->idx + 14;
 	}
+	if (rate->idx >= band->n_bitrates) {
+		WARN(1, "wrong rate->idx value: %d", rate->idx);
+		return -1;
+	}
 	// WFx only support 2GHz, else band information should be retrieved
 	// from ieee80211_tx_info
 	band = wdev->hw->wiphy->bands[NL80211_BAND_2GHZ];