Fix code warning.

Change-Id: Ib11fb49f528d3688351ae349d5b4e307c28b3967
diff --git a/mbtk/libmbtk_lib/audio/mbtk_wav.c b/mbtk/libmbtk_lib/audio/mbtk_wav.c
index ac4bed8..403db74 100755
--- a/mbtk/libmbtk_lib/audio/mbtk_wav.c
+++ b/mbtk/libmbtk_lib/audio/mbtk_wav.c
@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <fcntl.h>
 #include <errno.h>
+#include <stdlib.h>
 
 #include "mbtk_log.h"
 #include "mbtk_audio_internal.h"
@@ -122,7 +123,10 @@
         recorder_header.data_sz = recorver_data_count;
         recorder_header.riff_sz = recorder_header.data_sz + sizeof(recorder_header) - 8;
         lseek(wav_recorder_fd, 0, SEEK_SET);
-        write(wav_recorder_fd, &recorder_header, sizeof(struct wav_header));
+
+        if(sizeof(struct wav_header) == write(wav_recorder_fd, &recorder_header, sizeof(struct wav_header))) {
+            // Do nothting.
+        }
 
         close(wav_recorder_fd);
         wav_recorder_fd = -1;
@@ -177,7 +181,11 @@
         return -1;
     }
 
-    read(wav_play_fd, &riff_wave_header, sizeof(riff_wave_header));
+    if(sizeof(riff_wave_header) != read(wav_play_fd, &riff_wave_header, sizeof(riff_wave_header))) {
+        LOGE("%s: read riff_wave_header fail.", __FUNCTION__);
+        return -1;
+    }
+
     if ((riff_wave_header.riff_id != ID_RIFF) || (riff_wave_header.wave_id != ID_WAVE)) {
         LOGE("Error: '%s' is not a riff/wave file", path);
         close(wav_play_fd);
@@ -185,11 +193,17 @@
     }
 
     do {
-        read(wav_play_fd, &chunk_header, sizeof(chunk_header));
+        if(sizeof(chunk_header) != read(wav_play_fd, &chunk_header, sizeof(chunk_header))) {
+            LOGE("%s: read chunk_header fail.", __FUNCTION__);
+            return -1;
+        }
 
         switch (chunk_header.id) {
             case ID_FMT:
-                read(wav_play_fd, &chunk_fmt, sizeof(chunk_fmt));
+                if(sizeof(chunk_fmt) != read(wav_play_fd, &chunk_fmt, sizeof(chunk_fmt))) {
+                    LOGE("%s: read chunk_fmt fail.", __FUNCTION__);
+                    return -1;
+                }
                 /* If the format header is larger, skip the rest */
                 if (chunk_header.sz > sizeof(chunk_fmt))
                     lseek(wav_play_fd, chunk_header.sz - sizeof(chunk_fmt), SEEK_CUR);
@@ -353,7 +367,6 @@
 
 int mbtk_audio_wav_recorder_start(const void *wav_file, mbtk_audio_sample_rate_enum sample_rate)
 {
-    int rc;
     const char *path = (const char *)wav_file;
 
     LOGD("wav_file is %s.", path);