ALSA: hda/cs8409: Fix possible NULL dereference

In the Linux kernel, the following vulnerability has been resolved: 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.