fs/xattr.c: fix simple_xattr_list()

fs/xattr.c: fix simple_xattr_list()

commit 8b0ba61df5a1 ("fs/xattr.c: fix simple_xattr_list to always
include security.* xattrs") failed to reset err after the call to
security_inode_listsecurity(), which returns the length of the
returned xattr name. This results in simple_xattr_list() incorrectly
returning this length even if a POSIX acl is also set on the inode.

Reported-by: Collin Funk <collin.funk1@gmail.com>
Closes: https://lore.kernel.org/selinux/8734ceal7q.fsf@gmail.com/
Reported-by: Paul Eggert <eggert@cs.ucla.edu>
Closes: https://bugzilla.redhat.com/show_bug.cgi?id=2369561
Fixes: 8b0ba61df5a1 ("fs/xattr.c: fix simple_xattr_list to always include security.* xattrs")
Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Link: https://lore.kernel.org/20250605165116.2063-1-stephen.smalley.work@gmail.com
Signed-off-by: Christian Brauner <brauner@kernel.org>