crypto: Change the qcrypto_random_bytes buffer type to void*

crypto: Change the qcrypto_random_bytes buffer type to void*

Using uint8_t* merely requires useless casts for use with
other types to be filled with randomness.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>