Fix some code which causes warnings when compiled by /analyze tool

core/fxcodec/codec/fx_codec_png.cpp

Index: core/fxcodec/codec/fx_codec_png.cpp
diff --git a/core/fxcodec/codec/fx_codec_png.cpp b/core/fxcodec/codec/fx_codec_png.cpp
index 61d4cebdbba28aa3ab2fc363232b848e75c51fc0..f7b922973eb590c72ef039edfcae88a1f43fe720 100644
--- a/core/fxcodec/codec/fx_codec_png.cpp
+++ b/core/fxcodec/codec/fx_codec_png.cpp
@@ -56,7 +56,7 @@ static void _png_load_bmp_attribute(png_structp png_ptr,
     if (t) {
       FXSYS_memset(pAttribute->m_strTime, 0, sizeof(pAttribute->m_strTime));
       FXSYS_snprintf((FX_CHAR*)pAttribute->m_strTime,
-                     sizeof(pAttribute->m_strTime), "%4d:%2d:%2d %2d:%2d:%2d",
+                     sizeof(pAttribute->m_strTime), "%4u:%2u:%2u %2u:%2u:%2u",
                      t->year, t->month, t->day, t->hour, t->minute, t->second);
       pAttribute->m_strTime[sizeof(pAttribute->m_strTime) - 1] = 0;
       bTime = 1;