vlc: update opencv disabling flag

This patch completes the commit d7f13e500e5970577e7abd96a0e9254a1e8f643f
turning --{with,without}- options in --{enable,disable}- options.

Fixes:
  http://autobuild.buildroot.net/results/a34/a34abdcc92a6b2cf976760d66adf6c7572743bb4/

Signed-off-by: Samuel Martin <s.martin49@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/vlc/vlc.mk

@@ -42,7 +42,7 @@ VLC_CONF_OPT += \
 	--disable-projectm \
 	--disable-vsxu \
 	--disable-mtp \
-	--without-opencv
+	--disable-opencv
 
 # Building static and shared doesn't work, so force static off.
 ifeq ($(BR2_PREFER_STATIC_LIB),)