mmc: block: refactor mmc_blk_rw_try_restart()

The mmc_blk_rw_start_new() was named after the label inside
mmc_blk_issue_rw_rq() but is really a confusing name for this
function: what it does is to try to restart the latest issued
command on the host and card of the current MMC queue.

So rename it mmc_blk_rw_try_restart() that reflects what it
is doing and at this point also refactore the function to
treat the removed card as an exception and just exit if this
happens and run on in the function if that is not happening.

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