mmc: host: Prepare host drivers for mmc_regulator_set_vqmmc() returning > 0

Patch all drivers which use mmc_regulator_set_vqmmc() and prepare them for
the fact that mmc_regulator_set_vqmmc() can return a value > 0, which would
happen if the signal voltage switch did NOT happen, because the voltage was
already set correctly.

Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20200416163649.336967-1-marex@denx.de


[Ulf: Re-worked/simplified the code a bit]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>