mmc: core: Return 1 from mmc_regulator_set_vqmmc() if switch skipped

Adjust mmc_regulator_set_vqmmc() to return 1 if the voltage switch was
skipped because the regulator voltage was already correct. This allows
drivers to detect such condition and possibly skip various voltage
switching extras.

Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://lore.kernel.org/r/20200416163649.336967-2-marex@denx.de


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>