ASoC: rt5651: Do not modify the LDO voltage control bits from set_bias_level()

The PWR_ANLG1 reg not only contains various power on/off bits, it also
contains 2 bits which select if the LDO generates 1.0, 1.1 or 1.2V. Note
there is a separate on/off bit for the LDO.

rt5651_set_bias_level(BIAS_OFF) used to unconditionally clear the entire
register, when jack-detection support was introduced a special case for
jack-detect was added which hard-codes a register value to keep the LDO
voltage at 1.2 volt.

This commit removes the jack-detect special case, instead simply always
leaving the LDO voltage control bits as is on BIAS_OFF.

Tested-by: Carlo Caione <carlo@endlessm.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mark Brown <broonie@kernel.org>