Both the sys_hps.f2sdram_clock and the sys_dma_clk.clk signal are in the
same clock domain. They are both driven by the same clock. And even though
qsys is capable of detecting this it seems qsys interconnect is not able to
infer this and inserts a extra clock domain crossing bridge between the DMA
and the HPS AXI system memory interface.
To avoid this connect the sys_dma_clk.clk to the sys_hps.f2sdram_clock so
that all components are driven by the same qsys clock signal.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>