hwrng: hwrandom:
cleanup in hwrng_register()
add randomness to system from rng sources
fetch randomness only after device init
free rng_buffer at module exit

Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>