ARM: dts: imx6ull-tarragon: fix USB over-current polarity

Our Tarragon platform uses a active-low signal to inform
the i.MX6ULL about the over-current detection.

Fixes: 5e4f393c ("ARM: dts: imx6ull: Add chargebyte Tarragon support")
Signed-off-by: Michael Heimpold <michael.heimpold@chargebyte.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>