util: do not assign return value if it is not used (#10552)

src/basic/stat-util.c

@@ -47,10 +47,8 @@ int is_dir(const char* path, bool follow) {
 
 int is_dir_fd(int fd) {
         struct stat st;
-        int r;
 
-        r = fstat(fd, &st);
-        if (r < 0)
+        if (fstat(fd, &st) < 0)
                 return -errno;
 
         return !!S_ISDIR(st.st_mode);