xen: use the pirq number to check the pirq_eoi_map

In pirq_check_eoi_map use the pirq number rather than the Linux irq
number to check whether an eoi is needed in the pirq_eoi_map.

The reason is that the irq number is not always identical to the
pirq number so if we wrongly use the irq number to check the
pirq_eoi_map we are going to check for the wrong pirq to EOI.

As a consequence some interrupts might not be EOI'ed by the
guest correctly.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Tested-by: Tobias Geiger <tobias.geiger@vido.info>
[v1: Added some extra wording to git commit]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>