thermal: power_allocator: Use temperature reading from tz

All thermal governors use the temperature value stored in
struct thermal_zone_device.

   thermal_zone_device->temperature

power_allocator governor should not deviate from this and use
the same.

Cc: Javi Merino <javi.merino@arm.com>
Cc: Eduardo Valentin <edubezval@gmail.com>
Cc: Daniel Kurtz <djkurtz@chromium.org>
Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Javi Merino <javi.merino@arm.com>
Reported-by: Sugumar Natarajan <sugumar.natarajan@arm.com>
Signed-off-by: Kapileshwar Singh <kapileshwar.singh@arm.com>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>