use AV_RB32, swf_mp3_info may be replaced with mpa_decoder_header

Originally committed as revision 8123 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/swf.c

@@ -118,8 +118,7 @@ static const int sBitsPerSlot[3] = {
 
 static int swf_mp3_info(void *data, int *byteSize, int *samplesPerFrame, int *sampleRate, int *isMono )
 {
-    uint8_t *dataTmp = (uint8_t *)data;
-    uint32_t header = ( (uint32_t)dataTmp[0] << 24 ) | ( (uint32_t)dataTmp[1] << 16 ) | ( (uint32_t)dataTmp[2] << 8 ) | (uint32_t)dataTmp[3];
+    uint32_t header = AV_RB32(data);
     int layerID = 3 - ((header >> 17) & 0x03);
     int bitRateID = ((header >> 12) & 0x0f);
     int sampleRateID = ((header >> 10) & 0x03);