ASoC: mxs: Add .owner to struct snd_soc_card

Add missing .owner of struct snd_soc_card. This prevents the module from being
removed from underneath its users.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>