UPSTREAM: exfat: fix just enough dentries but allocate a new cluster to dir

This commit fixes the condition for allocating cluster to parent
directory to avoid allocating new cluster to parent directory when
there are just enough empty directory entries at the end of the
parent directory.

Bug: 254441685
Fixes: af02c72d ("exfat: convert exfat_find_empty_entry() to use dentry cache")
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
(cherry picked from commit 6697f819)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I36089d595d9957ec70fe2ff15900d068cad21e8f