mmc: sdhci: drop useless sdhci_get_compatibility() !OF stub

mmc: sdhci: drop useless sdhci_get_compatibility() !OF stub

The sdhci_get_compatibility() uses OF functions which have stubs for !OF
case, thus entire CONFIG_OF ifdef can be dropped.  This also fixes
!CONFIG_OF W=1 warning:

  drivers/mmc/host/sdhci-pltfm.c:76:6: error: no previous prototype for ‘sdhci_get_compatibility’ [-Werror=missing-prototypes]

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230314203901.20803-1-krzysztof.kozlowski@linaro.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>