ARM: dts: am437x-sk: fix lcd enable pin mux data

Caused by a copy & paste error. Note that even with
this bug AM437x SK display still works because GPIO
mux mode is always enabled. It's still wrong to mux
somebody else's pin.

Luckily ball D25 (offset 0x238 - gpio5_8) on AM437x
isn't used for anything.

While at that, also replace a pullup with a pulldown
as that gpio should be normally low, not high.

Cc: <stable@vger.kernel.org> # v3.17+
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>