media: v4l2-ctrls: Fix off-by-one error in integer menu control check

The V4L2 API defines the maximum value for an integer menu control as
the number of elements minus one. The v4l2_ctrl_new_std_menu() validates
this constraint with an off-by-one error. Fix it.

Fixes: d1e9b7c1 ("[media] V4L: Add support for integer menu controls with standard menu items")
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>