ACPI: detect invalid argument written to /proc/acpi/alarm

/proc/acpi/alarm can't be set correctly, here is a sample:

[root@localhost /]# echo "2006 09" > /proc/acpi/alarm
[root@localhost /]# cat /proc/acpi/alarm
2007-12-09 09:09:09
[root@localhost /]# echo "2006 04" > /proc/acpi/alarm
[root@localhost /]# cat /proc/acpi/alarm
2007-12-04 04:04:04
[root@localhost /]#

Obviously, it is wrong, it should consider it as an invalid input.

after this patch:

[root@localhost /]# echo "2008 09" > /proc/acpi/alarm
-bash: echo: write error: Invalid argument
[root@localhost /]#

Signed-off-by: Yi Yang <yi.y.yang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>