stat-util: rename files_same() → inode_same()

Let's be more accurate about what this function does: it checks whether
the underlying reported inode is the same. Internally, this already uses
a better named stat_inode_same() call, hence let's similarly name the
wrapping function following the same logic.

Similar for files_same_at() and path_equal_or_same_files().

No code changes, just some renaming.

src/basic/virt.c

@@ -891,7 +891,7 @@ int running_in_chroot(void) {
         if (getpid_cached() == 1)
                 return false;  /* We're PID 1, we can't be in a chroot. */
 
-        r = files_same("/proc/1/root", "/", 0);
+        r = inode_same("/proc/1/root", "/", 0);
         if (r == -ENOENT) {
                 r = proc_mounted();
                 if (r == 0) {