crypto: testmgr - fix RNG return code enforcement

Due to the change to RNGs to always return zero in success case, the
invocation of the RNGs in the test manager must be updated as otherwise
the RNG self tests are not properly executed any more.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Alexander Bergmann <abergmann@suse.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>