ALSA: dummy: Fix PCM format loop in proc output

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")
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200201080530.22390-3-tiwai@suse.de


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