ASoC: SOF: amd: Correct spaces in Makefile

A space should be put around "+=" in each line.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20240510073739.23541-1-tiwai@suse.de


Signed-off-by: Mark Brown <broonie@kernel.org>