mmc: core: Clarify code which deals with polling in __mmc_switch()

mmc: core: Clarify code which deals with polling in __mmc_switch()

The __mmc_switch() deserves a clean-up. In this step, let's move some code
outside of the do-while loop, which deal deals with the card busy polling.

This change simplifies the code in that sense that it becomes easier to follow
what is being executed during card busy polling, but it also gives a better
understanding for when polling isn't done.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
(cherry picked from commit cb26ce069ffa87a1d237d0288176aac8ff79bffa)

Conflicts:
	drivers/mmc/core/mmc_ops.c