register_vga_switcheroo() sets the PM ops from the hda structure which
is freed later in azx_free. Make sure that these ops are cleared.
Caught by KASAN, initially noticed due to a general protection fault.
Fixes: 246efa4a07 ("snd/hda: add runtime suspend/resume on optimus support (v4)")
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>