regulator: rtq2208: Fix incorrect buck converter phase mapping

Use the hidden bank RG to get the correct buck converter phase mapping.

Fixes: 85a11f55 ("regulator: rtq2208: Add Richtek RTQ2208 SubPMIC")
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://patch.msgid.link/ae3245aa713f76000dbd20b4ad6f66d30611d3b8.1742204502.git.cy_huang@richtek.com


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