ARM: Kirkwood: Fix missing sdio clock

We moved to declaring clk gates in DT. However, device which do not
yet have a DT binding need to have a clkdev alias. This was missing
for SDIO.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Stefan Peter <s.peter@mplch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>