libgpg-error: use <pkg>_CONFIG_SCRIPTS

libgpg-error installs a gpg-error-config script, but it wasn't fixed
up properly. Use the <pkg>_CONFIG_SCRIPTS to handle this.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: "Samuel Martin" <s.martin49@gmail.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>