ARM: dts: imx6sl-warp: Fix OTG roles

USBOTG1 always work on peripheral mode and USBOTG in host mode, so fix
their roles accordingly.

Tested by mounting the MMC card as a storage device:

modprobe g_mass_storage file=/dev/mmcblk0p2

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>