drbg_kcapi_sym_ctr() was using wait_for_completion_interruptible() to
wait for completion of async crypto op but if a signal occurs it
may return before DMA ops of HW crypto provider finish, thus
corrupting the output buffer.
Resolve this by using wait_for_completion() instead.
Reported-by: Eric Biggers <ebiggers3@gmail.com> Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com> CC: stable@vger.kernel.org Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>