permission: improve const-correctness

src/permission.c

@@ -111,7 +111,7 @@ void initPermissions(void)
 		permission_default = parsePermissions(param->value);
 }
 
-int getPermissionFromPassword(char *password, unsigned *permission)
+int getPermissionFromPassword(char const* password, unsigned* permission)
 {
 	bool found;
 	gpointer key, value;

src/permission.h

@@ -27,7 +27,7 @@
 #define PERMISSION_ADMIN   8
 
 
-int getPermissionFromPassword(char *password, unsigned *permission);
+int getPermissionFromPassword(char const* password, unsigned* permission);
 
 void finishPermissions(void);