ALSA: hda/cs8409: Fix possible NULL dereference

ALSA: hda/cs8409: Fix possible NULL dereference

If snd_hda_gen_add_kctl fails to allocate memory and returns NULL, then
NULL pointer dereference will occur in the next line.

Since dolphin_fixups function is a hda_fixup function which is not supposed
to return any errors, add simple check before dereference, ignore the fail.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 20e507724113 ("ALSA: hda/cs8409: Add support for dolphin")
Signed-off-by: Murad Masimov <m.masimov@maxima.ru>
Link: https://patch.msgid.link/20241010221649.1305-1-m.masimov@maxima.ru
Signed-off-by: Takashi Iwai <tiwai@suse.de>