usb: dwc3: gadget: properly check ep cmd

The cmd argument we pass to
dwc3_send_gadget_ep_cmd() could contain extra
arguments embedded. When checking for StartTransfer
command, we need to make sure to match only lower 4
bits which contain the actual command and ignore the
rest.

Reported-by: Janusz Dziedzic <januszx.dziedzic@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Git-commit: 5999914f227b20addf01297b3df24be6b4161f69
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>
Change-Id: Id6c1f63fc9f4ce312b4be0712c57e3cd22295eab