mmc: core: Let mmc_send_tuning() to take struct mmc_host* as parameter

To be able to use mmc_send_tuning() prior the struct mmc_card has been
allocated, let's convert it to take the struct mmc_host* as parameter
instead.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Dong Aisheng <b29396@freescale.com>
Reviewed-by: Stephen Boyd <sboyd@codeaurora.org>