thermal: Rename set_mode() to change_mode()

set_mode() is only called when tzd's mode is about to change. Actual
setting is performed in thermal_core, in thermal_zone_device_set_mode().
The meaning of set_mode() callback is actually to notify the driver about
the mode being changed and giving the driver a chance to oppose such
change.

To better reflect the purpose of the method rename it to change_mode()

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
[for acerhdf]
Acked-by: Peter Kaestle <peter@piie.net>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20200629122925.21729-12-andrzej.p@collabora.com