ASoC: core: Clarify usage of ignore_machine

For a sound card ignore_machine means that existing FEs links should be
ignored and existing BEs links should be overridden with some information
from the matching component driver.

Current code make some confusions about this so fix it!

Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Link: https://lore.kernel.org/r/20190925183358.11955-1-daniel.baluta@nxp.com


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