ASoC: sgtl5000: avoid division by zero if lo_vag is zero

ASoC: sgtl5000: avoid division by zero if lo_vag is zero

[ Upstream commit 9ab708aef61f5620113269a9d1bdb1543d1207d0 ]

In the case where lo_vag <= SGTL5000_LINE_OUT_GND_BASE, lo_vag
is set to zero and later vol_quot is computed by dividing by
lo_vag causing a division by zero error.  Fix this by avoiding
a zero division and set vol_quot to zero in this specific case
so that the lowest setting for i is correctly set.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>