Wrong switch case condition in get_storage_device_name() for virtio-blk interface type

[skoenig]

create-alpine-disk-image/lib/common-functions

Lines 768 to 769 in 3779349

	virtio_blk )
	_device_name="/dev/vda" ;;

The $_device_type to check against should be "virtio-blk" not "virtio_blk", as this is the string passed on with create-alpine-disk-image --os-device-type virtio-blk ...