usb: xhci-msm-hsic: flush pwr event completion during device removal

Race between hsic removal and hub suspend thread could result in
condition where suspend thread waits for 5 secs for power event irq
but hsic device already unregistered the irq. Avoid this race by
completing the completion variable during hsic removal.

Change-Id: I07deadd3bc0300bafc8899c2d47aeab178fa9fcc
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>