clock: Fix _STIME_FORMAT macros
clock: Fix _STIME_FORMAT macros

This macro didn't work well as it relied on the sign on the last
divided number (number of days). This value is most of the time
zero, and zero is considered positive in printf. Instead, deal with
the sign manually, and resuse the original macros for the rest. This
actually simplify the macro a lot.

centricular/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,centricular/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer