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

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

[ Upstream commit 6697f819a10b238ccf01998c3f203d65d8374696 ]

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.

Fixes: af02c72d0b62 ("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>
Signed-off-by: Sasha Levin <sashal@kernel.org>