wifi: mac80211_hwsim: set virtio device ready in probe()

Just like a similar commit to arch/um/drivers/virt-pci.c, call
virtio_device_ready() to make this driver work after commit
b4ec69d7e09 ("virtio: harden vring IRQ"), since the driver uses
the virtqueues in the probe function.  (The virtio core sets
the device ready when probe returns.)

Fixes: 8b4ec69d ("virtio: harden vring IRQ")
Fixes: 5d44fe7c

 ("mac80211_hwsim: add frame transmission support over virtio")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20220613210401.327958-1-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>