[media] dvb_usb_v2: remove usb_clear_halt()

Calling usb_clear_halt() during device init is not correct.
2 of 7 AF9015 devices I have timeouts next USB control message
after usb_clear_halt(). It was originally performed between
tuner_attach() and rc_query() and likely not causing problems
since rc_query() is repeated continously. None could see it when
first rc_query() failed...

Secondly it was not called for .generic_bulk_ctrl_endpoint_response.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>