Bluetooth: btnxpuart: Deasset UART break before closing serdev device

This adds a call to ps_wakeup() before closing the serdev device, to
de-assert UART break.

Signed-off-by: Neeraj Sanjay Kale <neeraj.sanjaykale@nxp.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>