MLK-14662 mmc: debugfs: add runtime pm when cat ios or clock file node

MLK-14662 mmc: debugfs: add runtime pm when cat ios or clock file node

MMC core code add 'MMC_CAP_RUNTIME_RESUME', postpone the real card
resume operation from bus_resume to bus_runtime_resume. So after
system resume, for non-removable-card, it still not really resume.
At this point, if user cat the ios or clock node, only get zero
data although the mmc/sd card is still present.

This patch add mmc_get_card() to make sure card really resume back
when user cat ios or clock debugfs file node, then user can get the
correct information.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>