hwrng: virtio - Virtio RNG devices need to be re-registered after suspend/resume

The patch for

commit: 5c062734
Author: Amit Shah <amit.shah@redhat.com>
Date:   Sun Jul 27 07:34:01 2014 +0930

    virtio: rng: delay hwrng_register() till driver is ready

moved the call to hwrng_register() out of the probe routine into the scan
routine. We need to call hwrng_register() after a suspend/restore cycle
to re-register the device, but the scan function is not invoked for the
restore. Add the call to hwrng_register() to virtio_restore().

Reviewed-by: Liam Merwick <Liam.Merwick@oracle.com>
Signed-off-by: Jim Quigley <Jim.Quigley@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>