mfd: intel_quark_i2c_gpio: Remove clock tree on error path

There is a potential resource leak in case when ->probe() fails. We have to
unregister and remove clock tree which is done here.

This is a follow up to previously pushed commit c4726abc ("mfd:
intel_quark_i2c_gpio: Use clkdev_create()") that prevents double free() when
clkdev_drop() followed by kfree() in devm_kcalloc() release stage.

I leave Fixes tag here, but the backporting will require to backport the commit
c4726abc ("mfd: intel_quark_i2c_gpio: Use clkdev_create()") first.

Cc: stable@vger.kernel.org
Fixes: 60ae5b9f (mfd: intel_quark_i2c_gpio: Add Intel Quark X1000 I2C-GPIO MFD Driver)
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>