serial: Add missing MODULE_DEVICE_TABLE

This patch adds missing MODULE_DEVICE_TABLE definition which generates
correct modalias for automatic loading of this driver when it is built
as an external module.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Bixuan Cui <cuibixuan@huawei.com>
Link: https://lore.kernel.org/r/20210410035048.11466-1-cuibixuan@huawei.com


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