package/vlc: Add optional dependency to zlib

zlib is an optional dependency of vlc:
http://git.videolan.org/gitweb.cgi?p=vlc.git;a=blob;f=configure.ac;h=d44151b3fb507141ce7f9b98e95fa11edcdaac01;hb=HEAD#l811

Thanks to Yann for pointing this out:
http://patchwork.ozlabs.org/patch/529248/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/vlc/vlc.mk

@@ -368,4 +368,8 @@ else
 VLC_CONF_OPTS += --without-x
 endif
 
+ifeq ($(BR2_PACKAGE_ZLIB),y)
+VLC_DEPENDENCIES += zlib
+endif
+
 $(eval $(autotools-package))