audio_processing: Create now returns a pointer to the object

Affects
* NS
* AGC
* AEC

BUG=441
TESTED=locally on Linux and trybots
R=kwiberg@webrtc.org

Review URL: https://codereview.webrtc.org/1175903002.

Cr-Commit-Position: refs/heads/master@{#9411}

webrtc/modules/audio_processing/ns/include/noise_suppression.h

@@ -20,20 +20,9 @@ extern "C" {
 #endif
 
 /*
- * This function creates an instance to the noise suppression structure
- *
- * Input:
- *      - NS_inst       : Pointer to noise suppression instance that should be
- *                        created
- *
- * Output:
- *      - NS_inst       : Pointer to created noise suppression instance
- *
- * Return value         :  0 - Ok
- *                        -1 - Error
+ * This function creates an instance of the floating point Noise Suppression.
  */
-int WebRtcNs_Create(NsHandle** NS_inst);
-
+NsHandle* WebRtcNs_Create();
 
 /*
  * This function frees the dynamic memory of a specified noise suppression