staging: wfx: drop unicode characters from strings

Smatch complains:

  hif_rx.c:235 hif_generic_indication() warn: format string contains non-ascii character '\xc2'
  hif_rx.c:235 hif_generic_indication() warn: format string contains non-ascii character '\xb0'
   234                  if (!wfx_api_older_than(wdev, 1, 4))
   235                          dev_info(wdev->dev, "Rx test ongoing. Temperature: %d°C\n",
                                                                                     ^
   236                                   body->data.rx_stats.current_temp);

So, replace the unicode character.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20201009171307.864608-8-Jerome.Pouiller@silabs.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/hif_rx.c

@@ -246,7 +246,7 @@ static int hif_generic_indication(struct wfx_dev *wdev,
 		mutex_lock(&wdev->rx_stats_lock);
 		// Older firmware send a generic indication beside RxStats
 		if (!wfx_api_older_than(wdev, 1, 4))
-			dev_info(wdev->dev, "Rx test ongoing. Temperature: %d°C\n",
+			dev_info(wdev->dev, "Rx test ongoing. Temperature: %d degrees C\n",
 				 body->data.rx_stats.current_temp);
 		memcpy(&wdev->rx_stats, &body->data.rx_stats,
 		       sizeof(wdev->rx_stats));