package/matchbox-keyboard: enforce disabling support for cairo

We usually explicitly enforce disabling optional support when it is
possible.

Do so for Cairo.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/matchbox-keyboard/matchbox-keyboard.mk

@@ -24,6 +24,7 @@ ifeq ($(BR2_PACKAGE_CAIRO),y)
 MATCHBOX_KEYBOARD_CONF_OPTS += --enable-cairo
 MATCHBOX_KEYBOARD_DEPENDENCIES += cairo
 else
+MATCHBOX_KEYBOARD_CONF_OPTS += --disable-cairo
 MATCHBOX_KEYBOARD_DEPENDENCIES += xlib_libXft
 endif