SACNT register should be marked volatile since
its WR and RD bits are cleared by SSI after
completing the relevant operation.
This unbreaks AC'97 register access.

Fixes: 05cf2379 ("ASoC: fsl_ssi: Add driver suspend and resume to support MEGA Fast")
Signed-off-by: NMaciej S. Szmigiero <mail@maciej.szmigiero.name>
Reviewed-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NMark Brown <broonie@kernel.org>