usb: common: otg-fsm: add license to usb-otg-fsm

Fix warning about tainted kernel because usb-otg-fsm has no license.
WARNING: with this patch usb-otg-fsm module can be loaded
but then the kernel will hang. Tested with a udoo quad board.

Cc: <stable@vger.kernel.org> #v4.1+
Signed-off-by: Oscar <oscar@naiandei.net>
Signed-off-by: Peter Chen <peter.chen@nxp.com>