tty: atmel_serial: Use of_property_present() for non-boolean properties

tty: atmel_serial: Use of_property_present() for non-boolean properties

The use of of_property_read_bool() for non-boolean properties is
deprecated in favor of of_property_present() when testing for property
presence.

As of_property_present() returns a boolean, use that directly
and simplify the code a bit while we're here.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Richard Genoud <richard.genoud@bootlin.com>
Reviewed-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20250109182053.3970547-1-robh@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>