GFX-Display: fix mistake in /proc/display_status.

GFX-Display: fix mistake in /proc/display_status.

BZ: 42140

system will hange ,when using /proc/display_status.

it is related to buf overflow ,which been not protected well.

one example:
echo "a b000 b100">/proc/display_status

cat /proc/display_status

Change-Id: I4695e6b8a9a31faaee6e437bbd0ae3e5d5b7900f
Signed-off-by: Ke Ai <ke.ai@intel.com>
Reviewed-on: http://android.intel.com:8080/53129
Reviewed-by: Xu, Randy <randy.xu@intel.com>
Tested-by: Tong, BoX <box.tong@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>