commit ffb80fc6 upstream.

At least macOS seems to be sending
ClearFeature(ENDPOINT_HALT) to endpoints which
aren't Halted. This makes DWC3's CLEARSTALL command
time out which causes several issues for the driver.

Instead, let's just return 0 and bail out early.
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>