ACPI: kill "unused variable ‘i’" warning

Commit 3d5b6fb4 ("ACPI: Kill overly
verbose "power state" log messages") removed the actual use of this
variable, but didn't remove the variable itself, resulting in build
warnings like

  drivers/acpi/processor_idle.c: In function ‘acpi_processor_power_init’:
  drivers/acpi/processor_idle.c:1169: warning: unused variable ‘i’

Just get rid of the now unused variable.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>