mmc: sdhci: Remove finish_tasklet

Remove finish_tasklet. Requests that require DMA-unmapping or sdhci_reset
are completed either in the IRQ thread or a workqueue if the completion is
not initiated by the IRQ.

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>