Update RT-Thread version to 5.2.1

Author: zhkag

include/rtdef.h

@@ -83,7 +83,7 @@ extern "C" {
 /* RT-Thread version information */
 #define RT_VERSION_MAJOR                5               /**< Major version number (X.x.x) */
 #define RT_VERSION_MINOR                2               /**< Minor version number (x.X.x) */
-#define RT_VERSION_PATCH                0               /**< Patch version number (x.x.X) */
+#define RT_VERSION_PATCH                1               /**< Patch version number (x.x.X) */
 
 /* e.g. #if (RTTHREAD_VERSION >= RT_VERSION_CHECK(4, 1, 0) */
 #define RT_VERSION_CHECK(major, minor, revise)          ((major * 10000U) + (minor * 100U) + revise)