regulator: mt6358: Fix vdram2 .vsel_mask

The valid vsel value are 0 and 12, so the .vsel_mask should be 0xf.

Signed-off-by: Hsin-Hsiung Wang <hsin-hsiung.wang@mediatek.com>
Reviewed-by: Axel Lin <axel.lin@ingics.com>
Link: https://lore.kernel.org/r/1624424169-510-1-git-send-email-hsin-hsiung.wang@mediatek.com


Signed-off-by: Mark Brown <broonie@kernel.org>