USB: uvc_video: Check for return value before halt bulk endpoint

Currently driver is trying to halt bulk endpoint when ep_queue
fails by checking endpoint type. If ep_queue and endpoint  disable
race each other, there is chance that NULL pointer dereference as
ep->desc which will be set to NULL in ep_disable callback. Fix it
by checking return value of ep_queue and try to halt only if return
value is not -ESHUTDOWN.

Change-Id: I2c8f20316c1b7fb9a1c6fc8f4409dd14c2f780c6
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>