usb: dwc3: gadget: return error if command sent to DEPCMD register fails

commit 76e838c9f7765f9a6205b4d558d75a66104bc60d upstream.

We need to return error to caller if command is not sent to
controller succesfully.

Change-Id: Ia78bc9e29a5049805f46210bbd2055aaf466c927
Signed-off-by: Subbaraya Sundeep Bhatta <sbhatta@xilinx.com>
Fixes: 72246da4 (usb: Introduce DesignWare USB3 DRD Driver)
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>