doc/filters: fix channel names in sofalizer example

Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -3511,10 +3511,10 @@ sofalizer=sofa=/path/to/ClubFritz12.sofa:type=freq:radius=2:rotation=5
 @end example
 
 @item
-Similar as above but with custom speaker positions for front left, front right, rear left and rear right
+Similar as above but with custom speaker positions for front left, front right, back left and back right
 and also with custom gain:
 @example
-"sofalizer=sofa=/path/to/ClubFritz6.sofa:type=freq:radius=2:speakers=FL 45|FR 315|RL 135|RR 225:gain=28"
+"sofalizer=sofa=/path/to/ClubFritz6.sofa:type=freq:radius=2:speakers=FL 45|FR 315|BL 135|BR 225:gain=28"
 @end example
 @end itemize