regulator: stm32-booster: Remove .min_uV and .list_voltage for fixed regulator

Setting .n_voltages = 1 and .fixed_uV is enough for fixed regulator,
remove the redundant .min_uV and .list_voltage settings.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Link: https://lore.kernel.org/r/20190723014102.25103-1-axel.lin@ingics.com
Signed-off-by: Mark Brown <broonie@kernel.org>