Fix spelling

compiler/rustc_mir_dataflow/src/value_analysis.rs

@@ -41,7 +41,7 @@ fn super_statement(&self, statement: &Statement<'tcx>, state: &mut State<Self::V
                 self.handle_assign(*place, rvalue, state);
             }
             StatementKind::SetDiscriminant { .. } => {
-                // Could tread this as writing a constant to a pseudo-place.
+                // Could treat this as writing a constant to a pseudo-place.
             }
             StatementKind::CopyNonOverlapping(..) => {
                 // FIXME: What to do here?