mmc: core: Remove unnecessary host claim

Callers already have the host claimed, so remove the unnecessary
calls to mmc_claim_host() and mmc_release_host().

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