Runtime: fix the incorrect platform info size (conformance).

Runtime: fix the incorrect platform info size (conformance).

As sizeof(str) already includes the '\0', we should not add 1
on the return size. Conformance case computeinfo could pass with
this patch.

(28-Aug 16:51:00)     BEGIN  Compute Info                            :
           ==>  CL_DEVICE_ERROR_CORRECTION_SUPPORT == 0
           ==>  CL_DEVICE_ERROR_CORRECTION_SUPPORT == 0
           ==>  CL_DEVICE_ERROR_CORRECTION_SUPPORT == 0
               PASSED computeinfo.

Signed-off-by: Zhigang Gong <zhigang.gong@linux.intel.com>
Reviewed-by: "Yang, Rong R" <rong.r.yang@intel.com>