usb: gadget: ci13xxx_udc: Fix test feature selector handling

The TEST_MODE SET_FEATURE setup request handling should setup the
status phase and write the test mode to the PORTSC_PTC field of
the PORTSC register, and then it should bail out. Currently, the
driver does so but in the absence of the case break, also goes on
to halt EP0 at the end.
Fix this by breaking the TEST_MODE case appropriately.

Change-Id: Ifccbdeaa5c57a0ba31e4025b7ad38e493de90403
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>