When AV/C command returns 'NOT IMPLEMENTED' status in its response, ALSA
oxfw driver uses ENOSYS as error code. However, it's expected just to be
used for missing system call number.

This commit replaces it with ENXIO.
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20200113073418.24622-2-o-takashi@sakamocchi.jpSigned-off-by: Takashi Iwai <tiwai@suse.de>