various: move const ptr indicator to return value

src/basic/filesystems.h

@@ -34,7 +34,7 @@ extern const FilesystemSet filesystem_sets[];
 
 const FilesystemSet *filesystem_set_find(const char *name);
 
-const char *fs_type_to_string(statfs_f_type_t magic);
+const char* fs_type_to_string(statfs_f_type_t magic);
 int fs_type_from_string(const char *name, const statfs_f_type_t **ret);
 bool fs_in_group(const struct statfs *s, enum FilesystemGroups fs_group);