cim: cim_df: drop ununsed variable vsyncstart
Fix compiler warning:
../src/cim/cim_df.c:1708:37: warning: variable 'vsyncstart' set but not used [-Wunused-but-set-variable] 1708 | unsigned long vsyncend, vtotal, vsyncstart; | ^~~~~~~~~~
Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net