crypto: drbg - Only fail when jent is unavailable in FIPS mode

When jent initialisation fails for any reason other than ENOENT,
the entire drbg fails to initialise, even when we're not in FIPS
mode.  This is wrong because we can still use the kernel RNG when
we're not in FIPS mode.

Change it so that it only fails when we are in FIPS mode.

Fixes: 57225e67 ("crypto: drbg - Use callback API for random readiness")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Reviewed-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>