mmc: card: fix asymmetric claim host in mmc_blk_ioctl_rpmb_cmd

On kernel-3.14 mmc_claim_host is replaced by mmc_get_card to also
call pm_runtime_get_sync.
mmc_blk_ioctl_rpmb_cmd has asymmetric claim and release as mmc_claim_host
was used to get the lock, but mmc_put_card was used for the release.
To fix this and prevent bad counter of runtime PM, mmc_claim_host
should be replaced with mmc_get_card.

Change-Id: I7c2218623fddfbeed0489aed330c9fe6e8bc5338
Signed-off-by: Maya Erez <merez@codeaurora.org>