package/libodb-mysql: fix static build with per-package directories

Fixes:
 - http://autobuild.buildroot.org/results/ba2c5ef1bb54c2751569f79beef21ff486348469

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit e3635ddda424c7b0d4c8f275de6db6f70219b2d9)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libodb-mysql/libodb-mysql.mk

@@ -12,6 +12,6 @@ LIBODB_MYSQL_INSTALL_STAGING = YES
 LIBODB_MYSQL_LICENSE = GPL-2.0
 LIBODB_MYSQL_LICENSE_FILES = LICENSE
 LIBODB_MYSQL_DEPENDENCIES = libodb mysql
-LIBODB_MYSQL_CONF_ENV = LIBS="$(shell $(STAGING_DIR)/usr/bin/mysql_config --libs)"
+LIBODB_MYSQL_CONF_ENV = LIBS=`$(STAGING_DIR)/usr/bin/mysql_config --libs`
 
 $(eval $(autotools-package))