Fix static analysis issue

'std::time_t' to 'long' may or may not override sign-bit depending on
size of implementation defined type
which may cause unexpected results on porting to different platforms

Change-Id: Ie4cfdc8f9e22e865d98b2b3ad2b918705f8beb5e
Signed-off-by: ilho kim <ilho159.kim@samsung.com>