ASoC: simple-card: code sync: rename num_link to num

simple sound card family are using very similar style, but because of its
historical reason, there are small differences. For example pointer style,
function name, caller postion etc...
This patch synchronized simple card style to other simple card family.

This patch renames num_link to num

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>