crypto: testmgr - Fix warning

crypto/testmgr.c: In function ‘test_cprng’:
crypto/testmgr.c:1204: warning: ‘err’ may be used uninitialized in this function

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>