avcodec/libfdk-aacenc: change MODE_7_1_FRONT_CENTER to map to AV_CH_LAYOUT_7POINT1_WIDE_BACK

This was suggested by Rodeo on IRC
<Rodeo> for consistency with the rest, MODE_7_1_FRONT_CENTER would be AV_CH_LAYOUT_7POINT1_WIDE_BACK (since LS+RS is mapped to back channels in other modes)
Reviewed-by: Jean First <jeanfirst@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libfdk-aacenc.c

@@ -394,7 +394,7 @@ static const uint64_t aac_channel_layout[] = {
     AV_CH_LAYOUT_4POINT0,
     AV_CH_LAYOUT_5POINT0_BACK,
     AV_CH_LAYOUT_5POINT1_BACK,
-    AV_CH_LAYOUT_7POINT1_WIDE,
+    AV_CH_LAYOUT_7POINT1_WIDE_BACK,
     AV_CH_LAYOUT_7POINT1,
     0,
 };