af_lavrresample: use a new libswresample function if available

It was recently added to libswresample, and it does exactly what we
need.

audio/filter/af_lavrresample.c

@@ -114,8 +114,12 @@ static void drop_all_output(struct af_resample *s)
 }
 static int get_out_samples(struct af_resample *s, int in_samples)
 {
+#if LIBSWRESAMPLE_VERSION_MAJOR > 1 || LIBSWRESAMPLE_VERSION_MINOR >= 2
+    return swr_get_out_samples(s->avrctx, in_samples);
+#else
     return av_rescale_rnd(in_samples, s->ctx.out_rate, s->ctx.in_rate, AV_ROUND_UP)
            + swr_get_delay(s->avrctx, s->ctx.out_rate);
+#endif
 }
 #endif