media: gl861: fix probe of dvb_usb_gl861

Probe of dvb_usb_gl861 was working at least with v4.4. Noticed the issue
with v4.13 but according to similar issues the problem started with v4.9.

[   15.288065] transfer buffer not dma capable
[   15.288090] WARNING: CPU: 2 PID: 493 at drivers/usb/core/hcd.c:1595 usb_hcd_map_urb_for_dma+0x4e2/0x640
...CUT...
[   15.288791] dvb_usb_gl861: probe of 3-7:1.0 failed with error -5

Tested with MSI Mega Sky 580 DVB-T Tuner [GL861]

[mchehab+samsung@kernel.org: rebased on the top of upstream]
Cc: stable@vger.kernel.org
Signed-off-by: Mika Båtsman <mika.batsman@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>

drivers/media/usb/dvb-usb-v2/gl861.c

@@ -26,10 +26,14 @@ static int gl861_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	if (wo) {
 		req = GL861_REQ_I2C_WRITE;
 		type = GL861_WRITE;
+		buf = kmemdup(wbuf, wlen, GFP_KERNEL);
 	} else { /* rw */
 		req = GL861_REQ_I2C_READ;
 		type = GL861_READ;
+		buf = kmalloc(rlen, GFP_KERNEL);
 	}
+	if (!buf)
+		return -ENOMEM;
 
 	switch (wlen) {
 	case 1:
@@ -42,24 +46,19 @@ static int gl861_i2c_msg(struct dvb_usb_device *d, u8 addr,
 	default:
 		dev_err(&d->udev->dev, "%s: wlen=%d, aborting\n",
 				KBUILD_MODNAME, wlen);
+		kfree(buf);
 		return -EINVAL;
 	}
-	buf = NULL;
-	if (rlen > 0) {
-		buf = kmalloc(rlen, GFP_KERNEL);
-		if (!buf)
-			return -ENOMEM;
-	}
+
 	usleep_range(1000, 2000); /* avoid I2C errors */
 
 	ret = usb_control_msg(d->udev, usb_rcvctrlpipe(d->udev, 0), req, type,
 			      value, index, buf, rlen, 2000);
-	if (rlen > 0) {
-		if (ret > 0)
+
+	if (!wo && ret > 0)
 		memcpy(rbuf, buf, rlen);
-		kfree(buf);
-	}
 
+	kfree(buf);
 	return ret;
 }