thermal: consider emul_temperature while computing trend

In case emulated temperature is in use, using the trend
provided by driver layer can lead to bogus situation.
In this case, debugger user would set a temperature value,
but the trend would be from driver computation.

To avoid this situation, this patch changes the get_tz_trend()
to consider the emulated temperature whenever that is in use.

Cc: Zhang Rui <rui.zhang@intel.com>
Cc: Amit Daniel Kachhap <amit.daniel@samsung.com>
Cc: Durgadoss R <durgadoss.r@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Eduardo Valentin <eduardo.valentin@ti.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>