ASoC: wm8990: Don't use range container for TLV with one entry

For TLVs with only a single entry it is not necessary to use a range
container. Use DECLARE_TLV_DB_SCALE() directly instead of a combination of
TLV_DB_RANGE_HEAD() and TLV_DB_SCALE_ITEM().

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>