package/ulogd: fix mysql build

Fix the following mysql build failure raised since bump to version 2.0.8
in commit 6fc4b59ffd3007ca9e436d33647acc5dfff62970:

checking for mysql_config... no
configure: error: libmysqlclient not found

Fixes:
 - http://autobuild.buildroot.org/results/a059be353b7464d4e6a7830a685b43bdd7ecd5fa

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
diff --git a/package/ulogd/ulogd.mk b/package/ulogd/ulogd.mk
index 7d4a1fd..033acb0 100644
--- a/package/ulogd/ulogd.mk
+++ b/package/ulogd/ulogd.mk
@@ -23,7 +23,9 @@
 ULOGD_CONF_OPTS += --disable-dbi
 endif
 ifeq ($(BR2_PACKAGE_MYSQL),y)
-ULOGD_CONF_OPTS += --enable-mysql
+ULOGD_CONF_OPTS += \
+	--enable-mysql \
+	--with-mysql-config=$(STAGING_DIR)/usr/bin/mysql_config
 ULOGD_DEPENDENCIES += mysql
 else
 ULOGD_CONF_OPTS += --disable-mysql