Fixes typo in Optical Flow PARAM (PX4#1658)

Thanks to @Ecuashungo for the report

PX4/docs.px4.io#23

en/sensor/optical_flow.md

@@ -12,7 +12,7 @@ An Optical Flow setup requires a downward facing camera and a [distance sensor](
 These can be connected via MAVLink, I2C or any other bus that supports the peripheral.
 
 :::note
-If connected to PX4 via MAVLink the Optical Flow device must publish to the [OPTICAL_FLOW_RAD](https://mavlink.io/en/messages/common.html#OPTICAL_FLOW_RAD) topic, and the distance sensor must publish to the [DISANCE_SENSOR](https://mavlink.io/en/messages/common.html#DISTANCE_SENSOR) topic.
+If connected to PX4 via MAVLink the Optical Flow device must publish to the [OPTICAL_FLOW_RAD](https://mavlink.io/en/messages/common.html#OPTICAL_FLOW_RAD) topic, and the distance sensor must publish to the [DISTANCE_SENSOR](https://mavlink.io/en/messages/common.html#DISTANCE_SENSOR) topic.
 :::
 
 The output of the flow when moving in different directions must be as follows: