ah4 input processing uses the asynchronous hash crypto API which
supplies an error code as part of the operation completion but
the error code was being ignored.

Treat a crypto API error indication as a verification failure.

While a crypto API reported error would almost certainly result
in a memcpy of the digest failing anyway and thus the security
risk seems minor, performing a memory compare on what might be
uninitialized memory is wrong.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>