SoC: rt274: Fix internal jack assignment in set_jack callback

When we call snd_soc_component_set_jack(component, NULL, NULL) we should
set rt274->jack to passed jack, so when interrupt is triggered it calls
snd_soc_jack_report(rt274->jack, ...) with proper value.

This fixes problem in machine where in register, we call
snd_soc_register(component, &headset, NULL), which just calls
rt274_mic_detect via callback.
Now when machine driver is removed "headset" will be gone, so we
need to tell codec driver that it's gone with:
snd_soc_register(component, NULL, NULL), but we also need to be able
to handle NULL jack argument here gracefully.
If we don't set it to NULL, next time the rt274_irq runs it will call
snd_soc_jack_report with first argument being invalid pointer and there
will be Oops.

Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>