bind: fix build with zlib

The bind configure.in now checks for "${with_zlib}/include/zlib.h".
Remove the redundant "include/".

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/bind/bind.mk

@@ -33,7 +33,7 @@ BIND_CONF_OPTS = \
 	--enable-filter-aaaa
 
 ifeq ($(BR2_PACKAGE_ZLIB),y)
-BIND_CONF_OPTS += --with-zlib=$(STAGING_DIR)/usr/include
+BIND_CONF_OPTS += --with-zlib=$(STAGING_DIR)/usr
 BIND_DEPENDENCIES += zlib
 else
 BIND_CONF_OPTS += --without-zlib