fan: Avoid reading tec_i every cycle pre v3.0

This is the last remaining tec_i read, involving vref.

src/channels.rs

@@ -525,9 +525,15 @@ impl<'a> Channels<'a> {
     }
 
     pub fn current_abs_max_tec_i(&mut self) -> ElectricCurrent {
+        if self.hwrev.major > 2 {
             max_by(self.get_tec_i(0).abs(),
                    self.get_tec_i(1).abs(),
                    |a, b| a.partial_cmp(b).unwrap_or(core::cmp::Ordering::Equal))
+        } else {
+            max_by(self.get_i(0).abs(),
+                   self.get_i(1).abs(),
+                   |a, b| a.partial_cmp(b).unwrap_or(core::cmp::Ordering::Equal))
+        }
     }
 }