thermal: bang-bang governor: act on lower trip boundary

thermal: bang-bang governor: act on lower trip boundary

With interrupt driven thermal zones we pass the lower and upper temperature
on which shall be acted, so in the governor we have to act on the exact lower
temperature to be consistent. Otherwise an interrupt may be generated on the
exact lower temperature, but the bang bang governor does not react.

Change-Id: Ic9dd855b0767d34b15505c1ff12ea99b76cdcea7
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>