staging: wfx: gpiod_get_value() can return an error

Smatch complains:

    hif_rx.c:98 hif_wakeup_indication() warn: 'gpiod_get_value(wdev->pdata.gpio_wakeup)' returns positive and negative
    bh.c:24 device_wakeup() warn: 'gpiod_get_value_cansleep(wdev->pdata.gpio_wakeup)' returns positive and negative

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20201009171307.864608-7-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/bh.c

@@ -21,7 +21,7 @@ static void device_wakeup(struct wfx_dev *wdev)
 
 	if (!wdev->pdata.gpio_wakeup)
 		return;
-	if (gpiod_get_value_cansleep(wdev->pdata.gpio_wakeup))
+	if (gpiod_get_value_cansleep(wdev->pdata.gpio_wakeup) >= 0)
 		return;
 
 	if (wfx_api_older_than(wdev, 1, 4)) {

drivers/staging/wfx/hif_rx.c

@@ -94,8 +94,8 @@ static int hif_startup_indication(struct wfx_dev *wdev,
 static int hif_wakeup_indication(struct wfx_dev *wdev,
 				 const struct hif_msg *hif, const void *buf)
 {
-	if (!wdev->pdata.gpio_wakeup
-	    || !gpiod_get_value(wdev->pdata.gpio_wakeup)) {
+	if (!wdev->pdata.gpio_wakeup ||
+	    gpiod_get_value(wdev->pdata.gpio_wakeup) == 0) {
 		dev_warn(wdev->dev, "unexpected wake-up indication\n");
 		return -EIO;
 	}