lavfi/transpose: add missing const options flags

Fixes ffmpeg -h filter=transpose

libavfilter/vf_transpose.c

@@ -260,10 +260,10 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
 
 static const AVOption transpose_options[] = {
     { "dir", "set transpose direction", OFFSET(dir), AV_OPT_TYPE_INT, { .i64 = TRANSPOSE_CCLOCK_FLIP }, 0, 7, FLAGS, "dir" },
-        { "cclock_flip", "rotate counter-clockwise with vertical flip", 0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CCLOCK_FLIP }, .unit = "dir" },
-        { "clock",       "rotate clockwise",                            0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CLOCK       }, .unit = "dir" },
-        { "cclock",      "rotate counter-clockwise",                    0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CCLOCK      }, .unit = "dir" },
-        { "clock_flip",  "rotate clockwise with vertical flip",         0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CLOCK_FLIP  }, .unit = "dir" },
+        { "cclock_flip", "rotate counter-clockwise with vertical flip", 0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CCLOCK_FLIP }, .flags=FLAGS, .unit = "dir" },
+        { "clock",       "rotate clockwise",                            0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CLOCK       }, .flags=FLAGS, .unit = "dir" },
+        { "cclock",      "rotate counter-clockwise",                    0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CCLOCK      }, .flags=FLAGS, .unit = "dir" },
+        { "clock_flip",  "rotate clockwise with vertical flip",         0, AV_OPT_TYPE_CONST, { .i64 = TRANSPOSE_CLOCK_FLIP  }, .flags=FLAGS, .unit = "dir" },
 
     { "passthrough", "do not apply transposition if the input matches the specified geometry",
       OFFSET(passthrough), AV_OPT_TYPE_INT, {.i64=TRANSPOSE_PT_TYPE_NONE},  0, INT_MAX, FLAGS, "passthrough" },