Fix Opus not decoding at correct rate

Fixed an issue whereby Opus files would decode at the original sampling
rate rather than the sampling rate of the Opus file itself which should
always be 48000.

[Opus Custom](https://wiki.xiph.org/OpusFAQ#What_is_Opus_Custom.3F) is
not supported.

Signed-off-by: Mahyar Koshkouei <deltabeard@users.noreply.github.com>

source/opus.c

@@ -53,7 +53,7 @@ out:
  */
 uint32_t rateOpus(void)
 {
-	return opusHead->input_sample_rate;
+	return 48000;
 }
 
 /**