lavc/vvc: Correct sps_num_subpics_minus1 minimum

The spec says "the value of sps_num_subpics_minus1 shall be in the
range of 0 to MaxSlicesPerAu − 1, inclusive."

Signed-off-by: Frank Plowman <post@frankplowman.com>
Signed-off-by: James Almer <jamrial@gmail.com>

libavcodec/cbs_h266_syntax_template.c

@@ -1130,7 +1130,7 @@ static int FUNC(sps)(CodedBitstreamContext *ctx, RWContext *rw,
 
     flag(sps_subpic_info_present_flag);
     if (current->sps_subpic_info_present_flag) {
-        ue(sps_num_subpics_minus1, 1, VVC_MAX_SLICES - 1);
+        ue(sps_num_subpics_minus1, 0, VVC_MAX_SLICES - 1);
         if (current->sps_num_subpics_minus1 > 0) {
             flag(sps_independent_subpics_flag);
             flag(sps_subpic_same_size_flag);