cam (mmc): only report 1.8V signaling once the bus has switched

[seuros]

Summary

On a host that advertises no 1.8V capability the voltage switch is never
attempted, yet the feature was still recorded and the card announce line
claimed 1.8V signaling while the bus stayed at 3.3V.

Set the feature only after the tran settings change requesting vccq_180 has
completed successfully, so that it describes the signaling level in use rather
than what the card offered. A host that cannot switch, or failure
now leaves the bus at 3.3V.

Test Plan

Observed in Raspberry Pi2/3/5

[bz]

I believe this is wrong. The 18V here is a card *feature* and the feature doesn't change with what the host supports.

The actual voltage of the bus, if I remember correctly, is in ios.vccq.

You could cross check that with camcontrol.