ACPI / processor: remove superfluous pr == NULL checks

The only acpi_processor_get_power_info_fadt() user
(acpi_processor_get_power_info()) dereferences pr before calling
the function.

The only acpi_processor_hotplug() user (acpi_cpu_soft_notify())
checks for pr == NULL before calling the function.

The only acpi_processor_cst_has_changed() user (acpi_processor_notify())
checks for pr == NULL before calling the function.

The only acpi_processor_power_init() user (__acpi_processor_start())
dereferences pr before calling the function.

Thus remove superfluous pr == NULL checks from affected functions.

Also:

While at it remove redundant brackets from acpi_processor_hotplug().

Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>