tree-wide: propagate error code from _from_string() functions

Now that we know we have something useful, no need to make an answer up.

src/basic/log.c

@@ -1085,7 +1085,7 @@ int log_set_target_from_string(const char *e) {
 
         t = log_target_from_string(e);
         if (t < 0)
-                return -EINVAL;
+                return t;
 
         log_set_target(t);
         return 0;
@@ -1096,7 +1096,7 @@ int log_set_max_level_from_string(const char *e) {
 
         t = log_level_from_string(e);
         if (t < 0)
-                return -EINVAL;
+                return t;
 
         log_set_max_level(t);
         return 0;

src/basic/unit-name.c

@@ -252,7 +252,7 @@ int unit_name_build(const char *prefix, const char *instance, const char *suffix
 
         type = unit_type_from_string(suffix + 1);
         if (type < 0)
-                return -EINVAL;
+                return type;
 
         return unit_name_build_from_type(prefix, instance, type, ret);
 }