smb3: fix caching of ctime on setxattr

commit 5923d668 upstream.

Fixes xfstest generic/728 which had been failing due to incorrect
ctime after setxattr and removexattr

Update ctime on successful set of xattr

Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>