RC_Channel: correct RC_set_override parameter name

This was just misnamed.  All callers appear to be passing ms in.

libraries/RC_Channel/RC_Channel.cpp

@@ -335,13 +335,13 @@ bool RC_Channel::in_trim_dz() const
     return is_bounded_int32(radio_in, radio_trim - dead_zone, radio_trim + dead_zone);
 }
 
-void RC_Channel::set_override(const uint16_t v, const uint32_t timestamp_us)
+void RC_Channel::set_override(const uint16_t v, const uint32_t timestamp_ms)
 {
     if (!rc().gcs_overrides_enabled()) {
         return;
     }
 
-    last_override_time = timestamp_us != 0 ? timestamp_us : AP_HAL::millis();
+    last_override_time = timestamp_ms != 0 ? timestamp_ms : AP_HAL::millis();
     override_value = v;
     rc().new_override_received();
 }

libraries/RC_Channel/RC_Channel.h

@@ -68,7 +68,7 @@ public:
     void       set_control_in(int16_t val) { control_in = val;}
 
     void       clear_override();
-    void       set_override(const uint16_t v, const uint32_t timestamp_us);
+    void       set_override(const uint16_t v, const uint32_t timestamp_ms);
     bool       has_override() const;
 
     int16_t    stick_mixing(const int16_t servo_in);