crypto: drbg - Fixes panic in wait_for_completion call

commit b61929c6 upstream.

Initialise ctr_completion variable before use.

Cc: <stable@vger.kernel.org>
Signed-off-by: Harsh Jain <harshjain.prof@gmail.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>