ACPI: irq: Fix some kernel-doc issues

The following commit change the second parameter of acpi_set_irq_model()
but forgot to update the function description. Let's fix it.

  commit 7327b16f ("APCI: irq: Add support for multiple GSI domains")

Also add description of parameter 'gsi' for
acpi_get_irq_source_fwhandle() to avoid the following build W=1 warning.

  drivers/acpi/irq.c:108: warning: Function parameter or member 'gsi' not described in 'acpi_get_irq_source_fwhandle'

Fixes: 7327b16f ("APCI: irq: Add support for multiple GSI domains")
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>