mmc: rtsx_usb_sdmmc: Don't runtime resume the device while changing led

In case the card has been powered off, it seems silly to continue to allow
the led to be updated. Instead let's forbid that, as it enables us to
prevent runtime resuming the device and thus avoids wasting energy.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>