ARM: mach-imx: sdhci-esdhc-imx: initialize DMA mask

With commit 7b91369b ("mmc: sdhci: Set DMA mask when adding host")
DMA access got disabled for device drivers with zero DMA mask property.
sdhci-esdhc-imx got blocked from DMA access by this.  Hence: initialize
the DMA mask to enable access again.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>