thermal: tegra: fix memory allocation

Fix memory allocation to store the pointers to
thermal_zone_device.

Signed-off-by: Wei Ni <wni@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Eduardo Valentin <edubezval@gmail.com>