ASoC: wm8991: fix wrong usage of DECLARE_TLV_DB_LINEAR()

As long as reading datasheet of WM8991, this driver includes wrong usage
of DECLARE_TLV_DB_LINEAR().

In "Table 6 Input PGA Volume Range", volume is represented in 5 bits by
1.5 dB/step between -16.5/30.0 dB. Thus, 'in_pga_tlv' should be dB step
representation.

In "Table 34 LOMIX and ROMIX Volume Range", volume is represented in three
bits by -3 dB/step from 0 to -21 dB. Thus, 'out_mix_tlv' should be dB step
represenation.

In "Table 36 LOPGA, ROPGA, LOUT, ROUT and SPKVOL Volume Range", volume is
represented in 7 bits by 1 dB/step from -73 to 6 dB, including mute. Thus,
'out_pga_tlv' should be dB step representation.

In "Table 26 Digital Volume Range", volume is represented in 8 bits by
3/8 dB/step from -71.625 to 0 dB. Thus, 'out_dac_tlv' should be dB step
representation.

In "Table 16 ADC Digital Volume Range", volume is represented in 8 bits by
3/8 dB/step from -71.625 to 17.625 dB. Thus, 'in_adc_tlv' should be dB step
representation.

In "Table 23 Digital Sidetone Volume", volume is represented in 5 bits by
3 dB/step from -36 to 0 dB. Thus, 'out_sidetone_tlv' should be dB step
representation.

In "Table 12 Left Input Mixer Volume Control", volume is represented in
3 bits by 3 dB/step from -12 to 6 dB

Totally, current implementation includes misuse of TLV-related macro.

This commit replaces usage of DECLARE_TLV_DB_LINEAR() with proper macros,
to give proper information to applications in user land.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>