ASoC: tas2552: Use consistent name for 'struct tas2552_data'

In tas2552_sw_shutdown() tas_data is used while the rest of the driver uses
tas2552 when dealing with the 'struct tas2552_data'

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>