acpica: ACPI_MAX_SLEEP should be 2 sec, not 20

This limit is a workaround for AML that sleeps too long,
but the workaround didn't work b/c of a typo.

https://bugzilla.kernel.org/show_bug.cgi?id=13195

Signed-off-by: Len Brown <len.brown@intel.com>
cc: stable@kernel.org # 2.6.35..3.0