wl1271: sdio: claim host only when doing IO

Do not maintain a persistent sdio_claim_host state. Instead,
claim host before doing IO and release host soon after.

This fixes several mmc deadlock scenarios, e.g. during
suspend/resume.

Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Acked-by: Luciano Coelho <luciano.coelho@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>