avcodec/ffv1enc: Fix assertion failure with non zero bits per sample

Fixes Ticket5736
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

(cherry picked from commit c1bfeda5a3)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ffv1enc.c

@@ -780,14 +780,12 @@ FF_ENABLE_DEPRECATION_WARNINGS
         s->colorspace = 1;
         s->transparency = 1;
         s->chroma_planes = 1;
-        if (!avctx->bits_per_raw_sample)
-            s->bits_per_raw_sample = 8;
+        s->bits_per_raw_sample = 8;
         break;
     case AV_PIX_FMT_0RGB32:
         s->colorspace = 1;
         s->chroma_planes = 1;
-        if (!avctx->bits_per_raw_sample)
-            s->bits_per_raw_sample = 8;
+        s->bits_per_raw_sample = 8;
         break;
     case AV_PIX_FMT_GBRP9:
         if (!avctx->bits_per_raw_sample)