Fix pr_perror() usage

When using pr_perror(), format string should not end with \n,
as it is added by the macro itself.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>