qdm2: initialize coeff_per_sb_select from bit_rate

The value of coeff_per_sb_select depends on the bit rate, not on
sub_sampling.
Also remove the calculation of tmp, no longer needed.

Fixes tickets #1868 and #742 (only audio part)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/qdm2.c

@@ -1862,18 +1862,9 @@ static av_cold int qdm2_decode_init(AVCodecContext *avctx)
     if ((tmp * 2240) < avctx->bit_rate)  tmp_val = 4;
     s->cm_table_select = tmp_val;
 
-    if (s->sub_sampling == 0)
-        tmp = 7999;
-    else
-        tmp = ((-(s->sub_sampling -1)) & 8000) + 20000;
-    /*
-    0: 7999 -> 0
-    1: 20000 -> 2
-    2: 28000 -> 2
-    */
-    if (tmp < 8000)
+    if (avctx->bit_rate <= 8000)
         s->coeff_per_sb_select = 0;
-    else if (tmp <= 16000)
+    else if (avctx->bit_rate < 16000)
         s->coeff_per_sb_select = 1;
     else
         s->coeff_per_sb_select = 2;