tree-wide: coccinelle fixes

Yet another batch of Coccinelle fixes.

src/nspawn/nspawn-bind-user.c

@@ -171,10 +171,8 @@ static int find_free_uid(const char *directory, uid_t max_uid, uid_t *current_ui
 
                 /* We want to use the UID also as GID, hence check for it in /etc/group too */
                 r = check_etc_group_collisions(directory, NULL, (gid_t) *current_uid);
-                if (r < 0)
+                if (r <= 0)
                         return r;
-                if (r == 0) /* free! yay! */
-                        return 0;
         }
 }
 

src/nspawn/nspawn.c

@@ -4091,7 +4091,7 @@ static int make_uid_map_string(
         int r;
 
         assert(n_bind_user_uid == 0 || bind_user_uid);
-        assert(offset == 0 || offset == 2); /* used to switch between UID and GID map */
+        assert(IN_SET(offset, 0, 2)); /* used to switch between UID and GID map */
         assert(ret);
 
         /* The bind_user_uid[] array is a series of 4 uid_t values, for each --bind-user= entry one