rsi: fix memory leak on buf and usb_reg_buf

In the cases where len is too long, the error return path fails to
kfree allocated buffers buf and usb_reg_buf.  The simplest fix is to
perform the sanity check on len before the allocations to avoid having
to do the kfree'ing in the first place.

Detected by CoverityScan, CID#1452258,1452259 ("Resource Leak")

Fixes: 59f73e2a ("rsi: check length before USB read/write register")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wireless/rsi/rsi_91x_usb.c

@@ -162,13 +162,13 @@ static int rsi_usb_reg_read(struct usb_device *usbdev,
 	u8 *buf;
 	int status = -ENOMEM;
 
+	if (len > RSI_USB_CTRL_BUF_SIZE)
+		return -EINVAL;
+
 	buf  = kmalloc(RSI_USB_CTRL_BUF_SIZE, GFP_KERNEL);
 	if (!buf)
 		return status;
 
-	if (len > RSI_USB_CTRL_BUF_SIZE)
-		return -EINVAL;
-
 	status = usb_control_msg(usbdev,
 				 usb_rcvctrlpipe(usbdev, 0),
 				 USB_VENDOR_REGISTER_READ,
@@ -207,13 +207,13 @@ static int rsi_usb_reg_write(struct usb_device *usbdev,
 	u8 *usb_reg_buf;
 	int status = -ENOMEM;
 
+	if (len > RSI_USB_CTRL_BUF_SIZE)
+		return -EINVAL;
+
 	usb_reg_buf  = kmalloc(RSI_USB_CTRL_BUF_SIZE, GFP_KERNEL);
 	if (!usb_reg_buf)
 		return status;
 
-	if (len > RSI_USB_CTRL_BUF_SIZE)
-		return -EINVAL;
-
 	usb_reg_buf[0] = (value & 0x00ff);
 	usb_reg_buf[1] = (value & 0xff00) >> 8;
 	usb_reg_buf[2] = 0x0;