ASoC: SOF: topology: Avoid open coded arithmetic in memory allocation

Use kcalloc() instead of kzalloc()+open coded multiplication.
This is safer and saves a few lines of code.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/3bbf03cfd1966bc6fb6dd0939e039fc161078a61.1647757329.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Mark Brown <broonie@kernel.org>