scsi: megasas: null terminate bios version buffer

While reading information via 'megasas_ctrl_get_info' routine,
a local bios version buffer isn't null terminated. Add the
terminating null byte to avoid any OOB access.

Reported-by: Li Qiang <liqiang6-s@360.cn>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
