serial: pch: Make push_rx() return void.

push_rx() returns always 0.

Make push_rx() return void.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/r/20240301215246.891055-15-bigeasy@linutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>