USB: gadget: f_adb: dequeue request on error in adb_read

USB: gadget: f_adb: dequeue request on error in adb_read

In adb_read(), if wait_event_interruptible() returns an error, we need to
remove the request from the EP queue.  Else, on the next call to adb_read(), we
will attempt to enqueue the request again, potentially corrupting the
queue.  This is what happens with musb_gadget_queue(), which does not check for
duplicate requests.

Signed-off-by: Iliyan Malchev <malchev@google.com>