ARM: pm: force non-zero return value from __cpu_suspend when aborting

Ensure that the return value from __cpu_suspend is non-zero when
aborting.  Zero indicates a successful suspend occurred.

Tested-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>