Use sizeof(char) instead of sizeof(char*) pass to pointer_delta

src/hotspot/share/memory/memoryReserver.cpp

@@ -429,7 +429,7 @@ ReservedSpace HeapReserver::Instance::try_reserve_range(char *highest_start,
   assert(is_aligned(highest_start, attach_point_alignment), "precondition");
   assert(is_aligned(lowest_start, attach_point_alignment), "precondition");
 
-  const size_t attach_range = pointer_delta(highest_start, lowest_start, sizeof(char*));
+  const size_t attach_range = pointer_delta(highest_start, lowest_start, sizeof(char));
   const size_t num_attempts_possible = (attach_range / attach_point_alignment) + 1;
   const size_t num_attempts_to_try   = MIN2((size_t)HeapSearchSteps, num_attempts_possible);
   const size_t num_intervals = num_attempts_to_try - 1;