scsi: initialise info object with appropriate size

While processing controller 'CTRL_GET_INFO' command, the routine
'megasas_ctrl_get_info' overflows the '&info' object size. Use its
appropriate size to null initialise it.

Reported-by: Qinghao Tang <luodalongde@gmail.com>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <alpine.LFD.2.20.1512211501420.22471@wniryva>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: P J P <ppandit@redhat.com>
