ASoC: Intel: Skylake: Fix NULL ptr dereference when unloading clk dev

ASoC: Intel: Skylake: Fix NULL ptr dereference when unloading clk dev

When driver is probed, we iterate over NHLT and check if clk entries are
present. For each such entry we call register_skl_clk and keep the
result in data->clk[].
Currently data->clk is sparsely indexed using NHLT table iterator, while
when freeing we use number of registered entries. Let's just use
data->avail_clk_cnt as index, so it can be reset back in
unregister_src_clk.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>