avutil/hwcontext_vulkan: Move AVVkFrame.internal to the end

This allows us to remove it by allocating AVVkFrameInternal
jointly with AVVkFrame.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavutil/hwcontext_vulkan.h

@@ -306,11 +306,6 @@ struct AVVkFrame {
      */
     uint64_t sem_value[AV_NUM_DATA_POINTERS];
 
-    /**
-     * Internal data.
-     */
-    struct AVVkFrameInternal *internal;
-
     /**
      * Describes the binding offset of each image to the VkDeviceMemory.
      * One per VkImage.
@@ -323,6 +318,11 @@ struct AVVkFrame {
      * One per VkImage.
      */
     uint32_t queue_family[AV_NUM_DATA_POINTERS];
+
+    /**
+     * Internal data. Not to be accessed by users in any way.
+     */
+    struct AVVkFrameInternal *internal;
 };
 
 /**