ASoC: tas2552: Correct the Speaker Driver Playback Volume (PGA_GAIN)

The last parameter for DECLARE_TLV_DB_SCALE() is to tell if the gain will
be muted or not when it is set to raw 0. IN this case it is not muted.
The PGA_GAIN is in 0-4 bits in the register. Fix the offset in the
SOC_SINGLE_TLV() for this.

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