libmount: (umount) make mnt_stat_mountpoin() usable for relative paths

# mount -o loop devicefile /mnt/test
 # umount devicefile
 umount: devicefile: not mounted.

Addresses: https://bugzilla.redhat.com/show_bug.cgi?id=1653781
Signed-off-by: Karel Zak <kzak@redhat.com>

libmount/src/utils.c

@@ -126,7 +126,7 @@ static int fstype_cmp(const void *v1, const void *v2)
 int mnt_stat_mountpoint(const char *target, struct stat *st)
 {
 #ifdef AT_NO_AUTOMOUNT
-	return fstatat(-1, target, st, AT_NO_AUTOMOUNT);
+	return fstatat(AT_FDCWD, target, st, AT_NO_AUTOMOUNT);
 #else
 	return stat(target, st);
 #endif