mmc: block: Change mmc_apply_rel_rw() to get block address from the request

mmc_apply_rel_rw() will be used by Software Command Queuing also. In that
case the command argument is not the block address so change
mmc_apply_rel_rw() to get block address from the request.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>