avcodec/vp8: Move fade_present from context to stack

It is only an auxiliary value used for parsing the VP7 frame header.
Reviewed-by: Peter Ross <pross@xvid.org>
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/vp8.c

@@ -580,6 +580,7 @@ static int vp7_decode_frame_header(VP8Context *s, const uint8_t *buf, int buf_si
     int height = s->avctx->height;
     int alpha = 0;
     int beta  = 0;
+    int fade_present = 1;
 
     if (buf_size < 4) {
         return AVERROR_INVALIDDATA;
@@ -681,7 +682,6 @@ static int vp7_decode_frame_header(VP8Context *s, const uint8_t *buf, int buf_si
 
     s->update_last          = 1;
     s->update_probabilities = 1;
-    s->fade_present         = 1;
 
     if (s->profile > 0) {
         s->update_probabilities = vp89_rac_get(c);
@@ -689,13 +689,13 @@ static int vp7_decode_frame_header(VP8Context *s, const uint8_t *buf, int buf_si
             s->prob[1] = s->prob[0];
 
         if (!s->keyframe)
-            s->fade_present = vp89_rac_get(c);
+            fade_present = vp89_rac_get(c);
     }
 
     if (vpx_rac_is_end(c))
         return AVERROR_INVALIDDATA;
     /* E. Fading information for previous frame */
-    if (s->fade_present && vp89_rac_get(c)) {
+    if (fade_present && vp89_rac_get(c)) {
         alpha = (int8_t) vp89_rac_get_uint(c, 8);
         beta  = (int8_t) vp89_rac_get_uint(c, 8);
     }

libavcodec/vp8.h

@@ -335,11 +335,6 @@ typedef struct VP8Context {
 
     int vp7;
 
-    /**
-     * Fade bit present in bitstream (VP7)
-     */
-    int fade_present;
-
     /**
      * Interframe DC prediction (VP7)
      * [0] VP8_FRAME_PREVIOUS