xfs: revert commit 8954c44f

The name passed into __xfs_xattr_put_listent is exactly namelen bytes
long and not null-terminated.  Passing namelen+1 to the strscpy function

    strscpy(offset, (char *)name, namelen + 1);

is therefore wrong.  Go back to the old code, which works fine because
strncpy won't find a null in @name and stops after namelen bytes.  It
really could be a memcpy call, but it worked for years.

Reported-by:  <syzbot+898115bc6d7140437215@syzkaller.appspotmail.com>
Fixes: 8954c44f ("xfs: use strscpy() to instead of strncpy()")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>