avcodec/vvc_ctu: align motion vector fields

Should fix "member access within misaligned address 0xf00 for type 'const union
av_alias64', which requires 8 byte alignment" errors as reported by GCC ubsan.

Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/vvc/vvc_ctu.h

@@ -193,7 +193,7 @@ typedef struct Mv {
 } Mv;
 
 typedef struct MvField {
-    DECLARE_ALIGNED(4, Mv, mv)[2];  ///< mvL0, vvL1
+    DECLARE_ALIGNED(8, Mv, mv)[2];  ///< mvL0, vvL1
     int8_t  ref_idx[2];             ///< refIdxL0, refIdxL1
     uint8_t hpel_if_idx;            ///< hpelIfIdx
     uint8_t bcw_idx;                ///< bcwIdx
@@ -202,7 +202,7 @@ typedef struct MvField {
 } MvField;
 
 typedef struct DMVRInfo {
-    DECLARE_ALIGNED(4, Mv, mv)[2];  ///< mvL0, vvL1
+    DECLARE_ALIGNED(8, Mv, mv)[2];  ///< mvL0, vvL1
     uint8_t dmvr_enabled;
 } DMVRInfo;