random: use proper return types on get_random_{int,long}_wait()

commit 7c3a8a1db5e03d02cc0abb3357a84b8b326dfac3 upstream.

Before these were returning signed values, but the API is intended to be
used with unsigned values.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>