rsi: fix a dereference on adapter before it has been null checked

The assignment of dev is dereferencing adapter before adapter has
been null checked, potentially leading to a null pointer dereference.
Fix this by simply moving the assignment of dev to a later point
after the sanity null check of adapter.

Detected by CoverityScan CID#1398383 ("Dereference before null check")

Fixes: dad0d04f ("rsi: Add RS9113 wireless driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/rsi/rsi_91x_usb.c

@@ -73,8 +73,7 @@ static int rsi_write_multiple(struct rsi_hw *adapter,
 			      u8 *data,
 			      u32 count)
 {
-	struct rsi_91x_usbdev *dev =
-		(struct rsi_91x_usbdev *)adapter->rsi_dev;
+	struct rsi_91x_usbdev *dev;
 
 	if (!adapter)
 		return -ENODEV;
@@ -82,6 +81,7 @@ static int rsi_write_multiple(struct rsi_hw *adapter,
 	if (endpoint == 0)
 		return -EINVAL;
 
+	dev = (struct rsi_91x_usbdev *)adapter->rsi_dev;
 	if (dev->write_fail)
 		return -ENETDOWN;