mysql: always replace paths in mysql_config script

Path replacement was not happening on some machines if the MySQL build
scripts set a different path in the produced mysql_config script,
resulting in host paths being left in.

Original patch by Joe Slater <jslater@windriver.com>.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>