ASoC: tas2552: fix dBscale-min declaration

The minimum volume level for the TAS2552 (control register value 0x00)
is -7dB however the driver declares it as -0.07dB.

Running amixer before the patch reports:
dBscale-min=-0.07dB,step=1.00dB,mute=0

Running amixer with the patch applied reports:
dBscale-min=-7.00dB,step=1.00dB,mute=0

Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org