ASoC: sgtl5000: Fix up define for SGTL5000_SMALL_POP

Currently, below code actually does not update any bit because
SGTL5000_SMALL_POP is 0.

snd_soc_update_bits(codec, SGTL5000_CHIP_REF_CTRL, SGTL5000_SMALL_POP, 1);

The SGTL5000_SMALL_POP should be BIT(0) rather than 0, fix it.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-By: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Mark Brown <broonie@kernel.org>