thinkpad-acpi: fix sign of ERESTARTSYS return

The returned error should be negative

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org>
Signed-off-by: Len Brown <len.brown@intel.com>