thermal/drivers/exynos: Fix an error code in exynos_tmu_probe()

This error path return success but it should propagate the negative
error code from devm_clk_get().

Fixes: 6c247393 ("thermal: exynos: Add TMU support for Exynos7 SoC")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210810084413.GA23810@kili