hw/pci/pci.c: Don't leak PCIBus::irq_count[] in pci_bus_irqs()

hw/pci/pci.c: Don't leak PCIBus::irq_count[] in pci_bus_irqs()

When calling pci_bus_irqs() multiple times on the same object without calling
pci_bus_irqs_cleanup() in between PCIBus::irq_count[] is currently leaked.
Let's fix this because Xen will do just that in a few commits, and because
calling pci_bus_irqs_cleanup() in between seems fragile and cumbersome.

Note that pci_bus_irqs_cleanup() now has to NULL irq_count such that
pci_bus_irqs() doesn't do a double free.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Chuck Zmudzinski <brchuckz@aol.com>
Message-Id: <20230403074124.3925-3-shentey@gmail.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>