arm64: dts: msm8998: thermal: Fix the gpu sensor number

The GPU sensor is sensor ID 13 on controller 0

Fixes: 4449b6f2 ("arm64: dts: qcom: msm8998: Add tsens and thermal-zones")
Signed-off-by: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Andy Gross <agross@kernel.org>