Change the macro from portMAX_DELAY to SIZE_MAX in order to initialize size_t-type variable correctly (#1310)

Author: du-yicheng23

portable/MemMang/heap_4.c

@@ -572,7 +572,7 @@ static void prvInsertBlockIntoFreeList( BlockLink_t * pxBlockToInsert ) /* PRIVI
 void vPortGetHeapStats( HeapStats_t * pxHeapStats )
 {
     BlockLink_t * pxBlock;
-    size_t xBlocks = 0, xMaxSize = 0, xMinSize = portMAX_DELAY; /* portMAX_DELAY used as a portable way of getting the maximum value. */
+    size_t xBlocks = 0, xMaxSize = 0, xMinSize = SIZE_MAX;
 
     vTaskSuspendAll();
     {

portable/MemMang/heap_5.c

@@ -672,7 +672,7 @@ void vPortDefineHeapRegions( const HeapRegion_t * const pxHeapRegions ) /* PRIVI
 void vPortGetHeapStats( HeapStats_t * pxHeapStats )
 {
     BlockLink_t * pxBlock;
-    size_t xBlocks = 0, xMaxSize = 0, xMinSize = portMAX_DELAY; /* portMAX_DELAY used as a portable way of getting the maximum value. */
+    size_t xBlocks = 0, xMaxSize = 0, xMinSize = SIZE_MAX;
 
     vTaskSuspendAll();
     {