dmaengine: sun6i: Remove obsolete clk muxing code

The sun6i DMA controller requires the AHB1 bus clock to be
clocked from PLL6. This was originally done by the dmaengine
driver during probe time. The AHB1 clock driver has since been
unified, so the original code does not work.

Remove the clk muxing code, and replace it with DT clk default
properties.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>