rtc: brcmstb-waketimer: add missed clk_disable_unprepare

commit 94303f89 upstream.

This driver forgets to disable and unprepare clock when remove.
Add a call to clk_disable_unprepare to fix it.

Fixes: c4f07ece ("rtc: brcmstb-waketimer: Add Broadcom STB wake-timer")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20191105160043.20018-1-hslester96@gmail.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>