vfio/migration: Add helper function to set state or reset device

vfio/migration: Add helper function to set state or reset device

There are several places where failure in setting the device state leads
to a device reset, which is done by setting ERROR as the recover state.

Add a helper function that sets the device state and resets the device
in case of failure. This will make the code cleaner and remove duplicate
comments.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>