doc/utils: fix atan2 parameter order

The C library function double atan2(double y, double x) takes y as the first
parameter and x as the second parameter.
Signed-off-by: Haixia Shi <hshi@meta.com>

doc/utils.texi

@@ -815,7 +815,7 @@ Compute arcsine of @var{x}.
 @item atan(x)
 Compute arctangent of @var{x}.
 
-@item atan2(x, y)
+@item atan2(y, x)
 Compute principal value of the arc tangent of @var{y}/@var{x}.
 
 @item between(x, min, max)