thermal: remove unnecessary call to thermal_zone_device_set_polling

When the thermal zone has no get_temp callback then thermal_zone_device_register()
calls thermal_zone_device_set_polling() with a polling delay of 0. This
only cancels the poll_queue. Since the poll_queue hasn't been scheduled this
is a no-op. Remove it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>