mmc: sdhci: Move some processing to __sdhci_finish_mrq()

In preparation for removing finish_tasklet, move some processing from
sdhci_request_done() to __sdhci_finish_mrq().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>