Fix malloc define typo

Fix compilation failure when SCTP is compiled due to incorrect define.

Reported-by: Conrad Kostecki <ck+gentoobugzilla@bl4ckb0x.de>
URL: https://bugs.gentoo.org/543828

RT#3758
Signed-off-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
