mariadb: update libdir for libtool

In mariadb recipe,do_install move all the lib files from usr/lib/mysql
to usr/lib,but didn't change libdir value in *.la libtool file. This
will cause libtool can't get correct lib path of mysql when other
package need mysql lib.So update them to correct value.

Here is a exapmle:
In libmysqlclient.la file: libdir = "/usr/lib/mysq/", but in fact
libmysqclient.so is installed into  "/usr/lib", this will cause
libtool can not find correct lib file with libmysqlclient.la, then
libtool will use rpath option to reference a absolute path, and
this will cause rpath WARING and rpm error.

Signed-off-by: Hongxu Jia <hongxu.jia@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>