mmc: mmci: Clear busy_status when starting command

If we are starting a command which can generate a busy
response, then clear the variable host->busy_status
if the variant is using a ->busy_complete callback.

We are lucky that the member is zero by default and
hopefully always gets cleared in the ->busy_complete
callback even on errors, but it's just fragile so
make sure it is always initialized to zero.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230405-pl180-busydetect-fix-v7-1-69a7164f2a61@linaro.org


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>