ALSA: firewire-motu: Correct a typo in the clock proc string

Just fix a typo of "S/PDIF" in the clock name string.

Fixes: 4638ec6e ("ALSA: firewire-motu: add proc node to show current statuc of clock and packet formats")
Acked-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Link: https://lore.kernel.org/r/20191030100921.3826-1-tiwai@suse.de


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