ASoC: Jack: Fix NULL pointer dereference in snd_soc_jack_report

Check for existance of jack before tracing.
NULL pointer dereference has been reported by KASAN while unloading
machine driver (snd_soc_cnl_rt274).

Signed-off-by: Pawel Harlozinski <pawel.harlozinski@linux.intel.com>
Link: https://lore.kernel.org/r/20191112130237.10141-1-pawel.harlozinski@linux.intel.com


Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org