mmc: mmc_spi: Use write_or_read temporary variable in mmc_spi_data_do()

Use write_or_read temporary variable in mmc_spi_data_do() to deduplicate
the conditional code.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20211206115218.73874-2-andriy.shevchenko@linux.intel.com


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