Quick fix to stop vpxdec infinite loop

vpxdec stays in a loop when decoding vp9.  This patch is a
quick fix to stop the loop when all data has been decoded.
Eventually we should move the vp9_get_raw_frame() call into
vp8_get_frame().

Change-Id: I3f97b6b4e1fe9ba69f746a29fc54c3304956f661

vp9/vp9_dx_iface.c

@@ -496,6 +496,7 @@ static vpx_image_t *vp8_get_frame(vpx_codec_alg_priv_t  *ctx,
       *iter = img;
     }
   }
+  ctx->img_avail = 0;
 
   return img;
 }