serial: drop irq-flags initialisations

There's no need to initialise irq-flags variables before saving the
interrupt state.

Drop the redundant initialisations from drivers that got this wrong.

Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210519092541.10137-1-johan@kernel.org


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