package/directfb: fixing typo in DIRECTFB_CONF_OPT

The DIRECTFB_CONF_OPT variable was missspelled for disabling the X11
support.

Signed-off-by: Carsten Schoenert <c.schoenert@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/directfb/directfb.mk

@@ -44,7 +44,7 @@ endif
 ifeq ($(BR2_PACKAGE_XSERVER),y)
 DIRECTFB_CONF_OPT += --enable-x11
 else
-DIRECTFB_CONF_OPT += -disable-x11
+DIRECTFB_CONF_OPT += --disable-x11
 endif
 
 ifeq ($(BR2_PACKAGE_DIRECTFB_UNIQUE),y)