spi: tegra20-slink: add missed clk_unprepare

commit 04358e40

 upstream.

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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>