evdev: any scroll device must have CAP_POINTER

evdev: any scroll device must have CAP_POINTER

Follow-up to e2f61b8fb74a06b86abd02caa4cdfde5edc53a32.

Scroll events are sent through the pointer interface, so we must set the
capability. Otherwise a caller may not have the required bits set up and is a
bit surprised by events coming out of an interface the device doesn't actually
have (xf86-input-libinput crashes when this happens).

Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>