mmc: sdhci-pxav2: remove unnecessary assignment of pltfm_host->priv

The sdhci_pltfm_init() function has initialized the priv member as
NULL, so there's no need to do it again.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>