mfd: arizona: Ensure 32k clock is put on driver unbind and error

Whilst it doesn't matter if the internal 32k clock register settings
are cleaned up on exit, as the part will be turned off losing any
settings, hence the driver hasn't historially bothered. The external
clock should however be cleaned up, as it could cause clocks to be
left on, and will at best generate a warning on unbind.

Add clean up on both the probe error path and unbind for the 32k
clock.

Fixes: cdd8da8c

 ("mfd: arizona: Add gating of external MCLKn clocks")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>