ASoC: cs35l35: Improve power down time

Shorten the time it takes to power down the amp by disabling the volume
ramp whilst doing the final shutdown. The driver has already muted the
amplifier at this stage so doing the volume ramp serves no purpose.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Brian Austin <brian.austin@cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>