ASoC: soc-component: Add comment for the endianness flag

Add a comment to make the purpose of the endianness flag on the
snd_soc_component structure more clear.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20220504170905.332415-2-ckeepax@opensource.cirrus.com


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