avcodec/error_resilience, mpeg12dec: Remove always-true checks

Having a decode_slice callback is mandatory for HWAccels;
the only exception to this (and the reason why these checks
were added) was XvMC, but it is no more since commit
be95df12bb.

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

libavcodec/error_resilience.c

@@ -804,7 +804,7 @@ void ff_er_frame_start(ERContext *s)
 
 static int er_supported(ERContext *s)
 {
-    if(s->avctx->hwaccel && s->avctx->hwaccel->decode_slice           ||
+    if (s->avctx->hwaccel ||
        !s->cur_pic.f                                                  ||
        s->cur_pic.field_picture
     )
@@ -828,7 +828,7 @@ void ff_er_add_slice(ERContext *s, int startx, int starty,
     const int end_xy   = s->mb_index2xy[end_i];
     int mask           = -1;
 
-    if (s->avctx->hwaccel && s->avctx->hwaccel->decode_slice)
+    if (s->avctx->hwaccel)
         return;
 
     if (start_i > end_i || start_xy > end_xy) {

libavcodec/mpeg12dec.c

@@ -1750,7 +1750,7 @@ static int mpeg_decode_slice(MpegEncContext *s, int mb_y,
         return AVERROR_INVALIDDATA;
     }
 
-    if (avctx->hwaccel && avctx->hwaccel->decode_slice) {
+    if (avctx->hwaccel) {
         const uint8_t *buf_end, *buf_start = *buf - 4; /* include start_code */
         int start_code = -1;
         buf_end = avpriv_find_start_code(buf_start + 2, *buf + buf_size, &start_code);