mmc: sdhci: Use more concise device_property_read_u64

Since we only need a single u64 the _array form is
unnecessarily. Use device_property_read_u64 instead.

Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20201125033630.603863-1-jeremy.linton@arm.com


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