ALSA: dummy: Fix PCM format loop in proc output

commit 2acf25f1 upstream.

The loop termination for iterating over all formats should contain
SNDRV_PCM_FORMAT_LAST, not less than it.

Fixes: 9b151fec

 ("ALSA: dummy - Add debug proc file")
Link: https://lore.kernel.org/r/20200201080530.22390-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>