gp8psk: fix gp8psk_usb_in_op() logic

Commit bc29131ecb10 ("[media] gp8psk: don't do DMA on stack") fixed the
usage of DMA on stack, but the memcpy was wrong for gp8psk_usb_in_op().
Fix it.

From Derek's email:
    "Fix confirmed using 2 different Skywalker models with
     HD mpeg4, SD mpeg2."

Suggested-by: Johannes Stezenbach <js@linuxtv.org>
Fixes: bc29131ecb10 ("[media] gp8psk: don't do DMA on stack")
Tested-by: Derek <user.vdr@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/media/usb/dvb-usb/gp8psk.c

@@ -67,7 +67,6 @@ int gp8psk_usb_in_op(struct dvb_usb_device *d, u8 req, u16 value, u16 index, u8
 		return ret;
 
 	while (ret >= 0 && ret != blen && try < 3) {
-		memcpy(st->data, b, blen);
 		ret = usb_control_msg(d->udev,
 			usb_rcvctrlpipe(d->udev,0),
 			req,
@@ -81,8 +80,10 @@ int gp8psk_usb_in_op(struct dvb_usb_device *d, u8 req, u16 value, u16 index, u8
 	if (ret < 0 || ret != blen) {
 		warn("usb in %d operation failed.", req);
 		ret = -EIO;
-	} else
+	} else {
 		ret = 0;
+		memcpy(b, st->data, blen);
+	}
 
 	deb_xfer("in: req. %x, val: %x, ind: %x, buffer: ",req,value,index);
 	debug_dump(b,blen,deb_xfer);