PCI: pciehp: Make queue_interrupt_event() void

Nobody looks at the return value from queue_interrupt_event(), so errors
were silently ignored.  Convert it to a "void" function and note the error
in the dmesg log.

No functional change except the new message.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rajat Jain <rajatja@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>