ARM: dts: am335x-sl50: Fix card detect pin for mmc1

The second version of the hardware moved the card detect pin from gpio0_6
to gpio1_9, as we won't support the first hardware version fix the pinmux
configuration of this pin.

Fixes: 8584d4fc ("ARM: dts: am335x-sl50: Add Toby-Churchill SL50 board support.")
Cc: <stable@vger.kernel.org> # 4.11
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>