scsi: mptsas: use g_new0 to allocate MPTSASRequest object

When processing IO request in mptsas, it uses g_new to allocate
a 'req' object. If an error occurs before 'req->sreq' is
allocated, It could lead to an OOB write in mptsas_free_request
function. Use g_new0 to avoid it.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <1473684251-17476-1-git-send-email-ppandit@redhat.com>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>