crypto: drbg - Fix ineffective sanity check

crypto: drbg - Fix ineffective sanity check

Fix drbg_healthcheck_sanity() to correctly check the return value of
drbg_generate().  drbg_generate() returns 0 on success, or a negative
errno value on failure.  drbg_healthcheck_sanity() incorrectly assumed
that it returned a positive value on success.

This didn't make the sanity check fail, but it made it ineffective.

Fixes: cde001e4c3c3 ("crypto: rng - RNGs must return 0 in success case")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>