mfd: intel-lpss: Remove clock tree on error path

We forgot to remove the clock tree if something goes wrong in ->probe(). Add a
call to intel_lpss_unregister_clock() on error path in ->probe() to fix the
potential issue.

Fixes: 4b45efe8 (mfd: Add support for Intel Sunrisepoint LPSS devices)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>