serial: lantiq: Use platform_get_irq() to get the interrupt

Use the preferred platform_get_irq() call to retrieve the interrupts. These
have the advantage of working with deferred probe and gets us one step
closer to removing of_irq_to_resource_table().

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211215224800.1984391-1-robh@kernel.org


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