regulator: Fix qcom-smd list voltage issues for msm8974

This commit looks like a cleanup but in fact by causing the core to go
down some simplified code paths for noop regulators it avoids a boot
time crash for msm8974 platforms which was introduced in v4.7.  It has
been in -next for a while, the issues in mainline for these platforms
weren't flagged up to me until yesterday (I think it took some time to
figure out what was going wrong).
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