net: qcom/emac: specify the correct DMA mask

The 64/32-bit DMA mask hackery in the EMAC driver is not actually necessary,
and is technically not accurate.  The EMAC hardware is limted to a 45-bit
DMA address.  Although no EMAC-enabled system can have that much DDR,
an IOMMU could possible provide a larger address.  Rather than play games
with the DMA mappings, the driver should provide a correct value and
trust the DMA/IOMMU layers to do the right thing.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Signed-off-by: David S. Miller <davem@davemloft.net>