[PATCH] acpi: Don't call acpi_sleep_prepare from acpi_power_off

Now that all of the code paths that call acpi_power_off
have been modified to call either call kernel_power_off
(which calls apci_sleep_prepare by way of acpi_shutdown)
or to call acpi_sleep_prepare directly it is redundant to call
acpi_sleep_prepare from acpi_power_off.

So simplify the code and simply don't call acpi_sleep_prepare.

In addition there is a little error handling done so if we
can't register the acpi class we don't hook pm_power_off.

I think I have done the right thing with the CONFIG_PM define
but I'm not certain.  Can this code even be compiled if
CONFIG_PM is false?

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>