ACPI: processor_throttling: Remove redundant initialization of 'obj'

'obj' is being initialized, however this value is never read as
'obj' is assigned an updated value later. Remove the redundant
initialization.

Clean up clang warning:
drivers/acpi/processor_throttling.c:409:20: warning: Value stored to
'obj' during its initialization is never read
[clang-analyzer-deadcode.DeadStores]

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>