lavfi/yadif: remove unnecessary cast

Finish what 99162f8d started
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_yadif.c

@@ -201,7 +201,7 @@ static int return_frame(AVFilterContext *ctx, int is_second)
     if (!yadif->csp)
         yadif->csp = av_pix_fmt_desc_get(link->format);
     if (yadif->csp->comp[0].depth_minus1 / 8 == 1)
-        yadif->filter_line = (void*)filter_line_c_16bit;
+        yadif->filter_line = filter_line_c_16bit;
 
     filter(ctx, yadif->out, tff ^ !is_second, tff);