mmc: sdhci-of-arasan: Convert to use np instead of pdev->dev.of_node

Use np pointer to simplify code and improve readability.

Signed-off-by: Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com>
Suggested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Link: https://lore.kernel.org/r/20210114152700.21916-3-muhammad.husaini.zulkifli@intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>