mmc: block: Use __mmc_send_status() and drop get_card_status()

The only reason to why the mmc block device driver needs to implements its
own version of how to get the status of the card, is that it needs to
specify a different amount of retries.

Therefore add a new exported function which allows the caller to specify
the number of retries and convert everybody to use it, as this simplifies
the code.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>