ASoC: acpi: fix: continue searching when machine is ignored

The machine_quirk may return NULL which means the acpi entries should be
skipped and search for next matched entry is needed, here add return
check here and continue for NULL case.

Signed-off-by: Keyon Jie <yang.jie@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>