usb: chipidea: otg: remove mutex unlock and lock while stop and start role

Wrongly release mutex lock during otg_statemachine may result in re-enter
otg_statemachine, which is not allowed, we should do next state transtition
after previous one completed.

Fixes: 826cfe75 ("usb: chipidea: add OTG fsm operation functions implementation")
Cc: <stable@vger.kernel.org> # v3.16+
Signed-off-by: Li Jun <jun.li@freescale.com>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>