fw_update: fix buffer overflow issue

fw_update: fix buffer overflow issue

BZ: 41666

Klocwork scan found a "Buffer Overflow in Bound String Copy" issue
in intel_scu_fw_update.c. This patch fix this issue.

Change-Id: Id328f616f079b42553ffc6cf1d50be3422880f9d
Signed-off-by: Li, Ning <ning.li@intel.com>
Reviewed-on: http://android.intel.com:8080/52601
Reviewed-by: Yang, Bin <bin.yang@intel.com>
Reviewed-by: Du, Alek <alek.du@intel.com>
Tested-by: Tang, HaifengX <haifengx.tang@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>