ARM: dts: colibri-imx6: specify usbh_pen gpio being active-low

Specify USBH_PEN GPIO being active-low rather than active-high.

Note that this should not have any functional impact as for fixed
regulators the regular GPIO polarity is ignored and a true active-high
enable GPIO would need an additional enable-active-high property which
is/was not the case here. However, this may be rather confusing which
this patch fixes.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>