pci: sprinkle assert in PCI pin number

pci: sprinkle assert in PCI pin number

If a device model
(a) doesn't set the value to a correct interrupt number and then
(b) triggers an interrupt for itself,
it's device model bug. Add assert on interrupt pin number to catch
this kind of bug more obviously.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Message-Id: <9cf8ac3b17e162daac0971d7be32deb6a33ae6ec.1616532563.git.isaku.yamahata@intel.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>