ARM: dts: msm: Specify the temperature sensor name for msm8996

Specify the name of GPU temperature sensor in the device tree.
This name is used to get the sensor's temperature by querying the
thermal driver API.

CRs-Fixed: 1064728
Change-Id: Ia93d93a442aa848cbd42a5fb8ecad5ef875f9abf
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>
Signed-off-by: Sunil Khatri <sunilkh@codeaurora.org>