i2c: virtio: mark device ready before registering the adapter

i2c: virtio: mark device ready before registering the adapter

virtio_i2c_probe() synchronously probes child i2c drivers on the bus,
but peripherals may use the bus at probe for tasks like reading a chip
id. The vhost-user-i2c backend stalls at such probes unless DRIVER_OK
is already set before the virtqueue is first kicked.

Set DRIVER_OK explicitly before i2c_add_adapter(), as done for the
same reason in commit f5866db64f34 ("virtio_console: enable VQs
early") and commit 71e4b8bf0482 ("virtio_rpmsg: set DRIVER_OK before
using device").

Signed-off-by: Alexis Bouzigues <BouziguesAlexis@JohnDeere.com>
Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>