spi: tegra20-slink: add missed clk_unprepare

The driver misses calling clk_unprepare in probe failure and remove.
Add the calls to fix it.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Link: https://lore.kernel.org/r/20191115083122.12278-1-hslester96@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>