mmc: omap-hsmmc: remove redundant null check

Because clk_disable_unprepare already checked NULL clock parameter, so the
additional checks are unnecessary, just remove them.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Link: https://lore.kernel.org/r/20200903084825.85616-1-vulab@iscas.ac.cn


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>