mmc: rtsx_usb_sdmmc: Avoid keeping the device runtime resumed when unused

The rtsx_usb_sdmmc driver may bail out in its ->set_ios() callback when no
SD card is inserted. This is wrong, as it could cause the device to remain
runtime resumed when it's unused. Fix this behaviour.

Tested-by: Ritesh Raj Sarraf <rrs@researchut.com>
Cc: <stable@vger.kernel.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>