arm64: dts: qcom: sm8550-mtp: Add missing supply for L1B regulator

Even though currently there is no consumer for L1B, add the supply
for it anyway.

Fixes: 71342fb9

 ("arm64: dts: qcom: Add base SM8550 MTP dts")
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20230801095246.2884770-1-abel.vesa@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>