tty: 8250_dw: Fix inverted arguments to serial_out in IRQ handler

commit 68e56cb3a068f9c30971c6117fbbd1e32918e49e upstream.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>