package/hplip: fix static linking with cups

Fixes
http://autobuild.buildroot.net/results/c52/c5277c42344d194e004dcd0a5af71bc6110da97e/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/hplip/hplip.mk

@@ -27,6 +27,9 @@ HPLIP_CONF_OPTS = \
 	--enable-new-hpcups \
 	--enable-lite-build
 
+# build system does not support cups-config
+HPLIP_CONF_ENV = LIBS=`$(STAGING_DIR)/usr/bin/cups-config --libs`
+
 ifeq ($(BR2_PACKAGE_DBUS),y)
 HPLIP_CONF_OPTS += --enable-dbus-build
 HPLIP_DEPENDENCIES += dbus