mmc: mmc_spi: Imply container_of() to be no-op

Since we don't use structure field layout randomization
the manual shuffling can affect some macros, in particular
container_of() against struct of_mmc_spi, which becomes
a no-op when pdata member is the first one in the structure.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210528112127.71738-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>