serial: 8250_dw: fall back to poll if there's no interrupt

[ Upstream commit 22130dae

 ]

When there's no irq(this can be due to various reasons, for example,
no irq from HW support, or we just want to use poll solution, and so
on), falling back to poll is still better than no support at all.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20230806092056.2467-3-jszhang@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Stable-dep-of: 87d80bfb

 ("serial: 8250_dw: Don't use struct dw8250_data outside of 8250_dw")
Signed-off-by: Sasha Levin <sashal@kernel.org>