ASoC: SOF: Turn "firmware boot complete" message into a dbg message

ASoC: SOF: Turn "firmware boot complete" message into a dbg message

Using a Canon Lake machine with the SOF driver causes dmesg to fill
up with a ton of these messages:

[  275.902194] sof-audio-pci 0000:00:1f.3: firmware boot complete
[  351.529358] sof-audio-pci 0000:00:1f.3: firmware boot complete
[  560.049047] sof-audio-pci 0000:00:1f.3: firmware boot complete
etc.

Since the DSP is powered down when not in used this happens everytime
e.g. a notification plays, polluting dmesg.

Turn this messages into a debug message, matching what the code already
does for the ""booting DSP firmware" message.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200402184948.3014-2-hdegoede@redhat.com
Signed-off-by: Mark Brown <broonie@kernel.org>