Replace reference to slspath with the complete URL of the source file

Without this change, importing map.jinja in config files (as opposed to
SLS files) causes a rendering error because `slspath` isn't defined.
The `salt_settings.key_url` variable gets used only in
`salt/pkgrepo/debian/init.sls`.

salt/map.jinja

@@ -11,7 +11,7 @@ that differ from whats in defaults.yaml
 {% set os_family_map = salt['grains.filter_by']({
     'Debian':  {
       'pkgrepo': 'deb http://debian.saltstack.com/debian ' + salt['grains.get']('oscodename') + '-saltstack main',
-      'key_url': 'salt://' + slspath + '/saltstack.gpg',
+      'key_url': 'salt://salt/pkgrepo/debian/saltstack.gpg',
       'libgit2': 'libgit2-22',
       'gitfs': {
         'pygit2': {