package/dhcp: add missing dependency on zlib

When BR2_PACKAGE_ZLIB=y, we enable zlib support in the bind included
in dhcp, but we forget to add zlib to DHCP_DEPENDENCIES, so it doesn't
get built before dhcp, causing build failures.

Fixes:

  http://autobuild.buildroot.net/results/5a33057ceaf3f53e6ba9deab3f214a4c8a644352/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/dhcp/dhcp.mk

@@ -45,6 +45,7 @@ DHCP_CONF_OPTS += --enable-delayed-ack
 endif
 
 ifeq ($(BR2_PACKAGE_ZLIB),y)
+DHCP_DEPENDENCIES += zlib
 DHCP_BIND_CONF_OPTS += --with-zlib
 else
 DHCP_BIND_CONF_OPTS += --without-zlib