hfsplus: fix generic/523 test-case failure

hfsplus: fix generic/523 test-case failure

The xfstests' test-case generic/523 fails to execute
correctly:

FSTYP -- hfsplus
PLATFORM -- Linux/x86_64 hfsplus-testing-0001 6.15.0-rc4+ #8 SMP PREEMPT_DYNAMIC Thu May 1 16:43:22 PDT 2025
MKFS_OPTIONS -- /dev/loop51
MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch

generic/523 - output mismatch (see xfstests-dev/results//generic/523.out.bad)

The test-case expects to have '/' in the xattr name.
However, HFS+ unicode logic makes conversion of '/'
into ':'. In HFS+, a filename can contain '/' because
':' is the separator. The slash is a valid filename
character on macOS. But on Linux, / is the path separator
and it cannot appear in a filename component. But xattr
name can contain any of these symbols. It means that
this unicode logic conversion doesn't need to be executed
for the case of xattr name.

This patch adds distinguishing the regular and xattr names.
If we have a regular name, then this conversion of special
symbols will be executed. Otherwise, the conversion is skipped
for the case of xattr names.

sudo ./check -g auto
FSTYP         -- hfsplus
PLATFORM      -- Linux/x86_64 hfsplus-testing-0001 7.0.0-rc1+ #24 SMP PREEMPT_DYNAMIC Fri Mar 20 12:36:49 PDT 2026
MKFS_OPTIONS  -- /dev/loop51
MOUNT_OPTIONS -- /dev/loop51 /mnt/scratch

<skipped>
generic/523 33s ...  25s
<skipped>

Closes: https://github.com/hfs-linux-kernel/hfs-linux-kernel/issues/178
cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
cc: Yangtao Li <frank.li@vivo.com>
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20260324003949.417048-2-slava@dubeyko.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>