mmc: core: Avoid hogging the CPU while polling for busy after I/O writes

mmc: core: Avoid hogging the CPU while polling for busy after I/O writes

When mmc_blk_card_busy() calls card_busy_detect() to poll for the card's
state with CMD13, this is done without any delays in between the commands
being sent.

Rather than fixing card_busy_detect() in this regards, let's instead
convert into using the common __mmc_poll_for_busy(), which also helps us to
avoid open-coding.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Link: https://lore.kernel.org/r/20210702134229.357717-4-ulf.hansson@linaro.org