doc: usb: ci-hdrc-usb2: add property over-current-active-high

Adding over-current-active-high to indicate the over current flag
is high active as typically we use active low for over current
polarity.

Signed-off-by: Li Jun <[e-mail]>
Signed-off-by: Peter Chen <[e-mail]>
Acked-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/usb/ci-hdrc-usb2.txt

···
 - fsl,usbmisc: phandler of non-core register device, with one
   argument that indicate usb controller index
 - disable-over-current: disable over current detect
+- over-current-active-high: over current signal polarity is high active,
+  typically over current signal polarity is low active.
 - external-vbus-divider: enables off-chip resistor divider for Vbus
 
 Example: