ALSA: hda: prevent undefined shift in snd_hdac_ext_bus_get_link()

This is harmless, but the "addr" comes from the user and it could lead
to a negative shift or to shift wrapping if it's too high.

Fixes: 0b00a561 ("ALSA: hdac_ext: add hdac extended controller")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20201103101807.GC1127762@mwanda


Signed-off-by: Takashi Iwai <tiwai@suse.de>