mmc: sdhci-of-at91: Use sdhci_pltfm_remove()

Use sdhci_pltfm_remove() instead of sdhci_pltfm_unregister() because
sdhci_pltfm_unregister() is going to be removed.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230811130351.7038-10-adrian.hunter@intel.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>