arm: mvebu: Fix pinctrl for Armada 370 Mirabox SDIO port.

The previous configuration used the wrong "clk" pin.  Without this
change mv_sdio worked because the bootloader would set the pin up, but
with a bootloader that does not set the pin, mv_sdio fails to detect any
card.

I have tested this change using a mwifiex_sdio wireless network adapter
over the SDIO interface.

Signed-off-by: Ryan Press <ryan@presslab.us>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>