collectd: unbreak collectd-mod-modbus

I tested it successfully on a Asus WL-500gP V2, querying
a Modbus TCP server.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>

utils/collectd/Makefile

@@ -298,7 +298,7 @@ $(eval $(call BuildPlugin,logfile,log files output,logfile,))
 $(eval $(call BuildPlugin,madwifi,MadWifi status input,madwifi,))
 #$(eval $(call BuildPlugin,mysql,MySQL status input,mysql,+PACKAGE_collectd-mod-mysql:libmysqlclient-r))
 $(eval $(call BuildPlugin,memory,physical memory usage input,memory,))
-$(eval $(call BuildPlugin,modbus,read variables through libmodbus,modbus,+PACKAGE_collectd-mod-modbus:libmodbus @BROKEN))
+$(eval $(call BuildPlugin,modbus,read variables through libmodbus,modbus,+PACKAGE_collectd-mod-modbus:libmodbus))
 $(eval $(call BuildPlugin,netlink,netlink input,netlink,+PACKAGE_collectd-mod-netlink:ip @BROKEN))
 $(eval $(call BuildPlugin,network,network input/output,network))
 $(eval $(call BuildPlugin,nginx,nginx status input,nginx,+PACKAGE_collectd-mod-nginx:libcurl))