f2fs: fix dcache lookup of !casefolded directories

Do the name comparison for non-casefolded directories correctly.

This is analogous to ext4's commit 66883da1eee8 ("ext4: fix dcache
lookup of !casefolded directories").

Fixes: 2c2eb7a300cd ("f2fs: Support case-insensitive file name lookups")
Cc: <stable@vger.kernel.org> # v5.4+
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>