ALSA: jack: don't report input event for phantom jack

There is no input_dev for phantom jack, we should not report
input event for it, otherwise, NULL pointer dereference error
will occur.

Fixes: 2ba2dfa1 ('ALSA: hda - Update to use the new jack kctls method')
Signed-off-by: Jie Yang <yang.jie@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>