mmc: sdhci: Add sdhci_cleanup_host

Add sdhci_cleanup_host() to cleanup __sdhci_add_host().

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Ludovic Desroches <ludovic.desroches@microchip.com>