fix ceil in lite demo (#5374)

deploy/lite/include/picodet_postprocess.h

@@ -20,6 +20,7 @@
 #include <utility>
 #include <ctime>
 #include <numeric>
+#include <math.h>
 
 #include "include/utils.h"
 
@@ -35,4 +36,4 @@ void PicoDetPostProcess(std::vector<PaddleDetection::ObjectResult>* results,
                          int num_class = 80,
                          int reg_max = 7);
 
-}  // namespace PaddleDetection
\ No newline at end of file
+}  // namespace PaddleDetection