mmc: core: Re-structure some code in __mmc_poll_for_busy()

To make the code a bit more understandable, let's move the check about
whether polling is allowed or not, out to the caller instead. In this way,
we can also drop the send_status in-parameter, so let's do that.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Acked-by: Avri Altman <avri.altman@wdc.com>
Link: https://lore.kernel.org/r/20210504161222.101536-4-ulf.hansson@linaro.org