mmc: meson-mx-sdhc: Don't use literal 0 to initialize structs

mmc: meson-mx-sdhc: Don't use literal 0 to initialize structs

Kbuild test robot reports the following warning in lines 56 and 87 of
drivers/mmc/host/meson-mx-sdhc-clkc.c:
  Using plain integer as NULL pointer

Drop the integer value from the struct initialization to fix that
warning. This will still ensure that the compiler will zero out the
struct so it's in a well-defined state.

Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://lore.kernel.org/r/20200517222907.1277787-2-martin.blumenstingl@googlemail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>