mmc: sdio: Keep card runtime resumed while adding function devices

Drivers core will runtime suspend a device with no driver. That means the
SDIO card will be runtime suspended as soon as it is added. It is then
runtime resumed to add each function. That is entirely pointless, so add
pm runtime get/put to keep the SDIO card runtime resumed until the function
devices have been added.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>