STAC/IDT driver calls snd_hda_jack_tbl_get() again after calling
snd_hda_jack_detect_enable_callback().  For simplifying this, let's
make snd_hda_jack_detect_enable_callback() returning the pointer while
handling the error with the standard IS_ERR() & co.
Signed-off-by: Takashi Iwai <tiwai@suse.de>