We see dwc3 endpoint stopped by unwanted irq during
suspend resume test, which is caused dwc3 ep can't be started
with error "No Resource".

Here, add synchronize_irq before suspend to sync the
pending IRQ handlers complete.
Signed-off-by: Bo He <bo.he@intel.com>
Signed-off-by: Yu Wang <yu.y.wang@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>