ARM: dts: am335x-evmsk: adjust mmc2 param to allow suspend

mmc2 used for wl12xx was missing the keep-power-in suspend
parameter. As a result the board couldn't reach suspend state.

Signed-off-by: Eyal Reizer <eyalr@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>