media: dvb-usb-v2: Fix incorrect use of transfer_flags URB_FREE_BUFFER

commit 1a0c10ed ("media: dvb-usb-v2: stop using coherent memory for
URBs") incorrectly adds URB_FREE_BUFFER after every urb transfer.

It cannot use this flag because it reconfigures the URBs accordingly
to suit connected devices. In doing a call to usb_free_urb is made and
invertedly frees the buffers.

The stream buffer should remain constant while driver is up.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
CC: stable@vger.kernel.org # v4.18+
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>