virtio-mmio: Reject invalid IRQ 0 command line argument

The "virtio_mmio.device=" command line argument allows a user to specify
the size, address, and IRQ of a virtio device.  Previously the only
requirement for the IRQ was that it be an unsigned integer.

Zero is an unsigned integer but an invalid IRQ number, and after
a85a6c86 ("driver core: platform: Clarify that IRQ 0 is invalid"),
attempts to use IRQ 0 cause warnings.

If the user specifies IRQ 0, return failure instead of registering a device
with IRQ 0.

Fixes: a85a6c86

 ("driver core: platform: Clarify that IRQ 0 is invalid")
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>