doc/indevs: fix x11grab options consistency

doc/indevs.texi

@@ -1352,17 +1352,13 @@ Set the video frame size. Default value is @code{vga}.
 Use the MIT-SHM extension for shared memory. Default value is @code{1}.
 It may be necessary to disable it for remote displays (legacy x11grab
 only).
-@end table
-
-@subsection @var{grab_x} @var{grab_y} AVOption
-
-The syntax is:
-@example
--grab_x @var{x_offset} -grab_y @var{y_offset}
-@end example
-
-Set the grabbing region coordinates. They are expressed as offset from the top left
-corner of the X11 window. The default value is 0.
 
+@item grab_x
+@item grab_y
+Set the grabbing region coordinates. They are expressed as offset from
+the top left corner of the X11 window and correspond to the
+@var{x_offset} and @var{y_offset} parameters in the device name. The
+default value for both options is 0.
+@end table
 
 @c man end INPUT DEVICES