Update naga/src/front/atomic_upgrade.rs

Simplify struct member upgrade.

Co-authored-by: Jim Blandy <jimb@red-bean.com>

naga/src/front/atomic_upgrade.rs

@@ -143,14 +143,9 @@ impl UpgradeState<'_> {
                 stride,
             },
             TypeInner::Struct { ref members, span } => {
-                let index = field_indices.pop().ok_or(Error::UnexpectedEndOfIndices)?;
-                let mut new_members = vec![];
-                for (i, mut member) in members.clone().into_iter().enumerate() {
-                    if i == index as usize {
-                        member.ty = self.upgrade_type(member.ty, field_indices)?;
-                    }
-                    new_members.push(member);
-                }
+                let index = field_indices.pop().ok_or(Error::UnexpectedEndOfIndices)? as usize;
+                let mut new_members = members.clone();
+                new_members[index].ty = self.upgrade_type(new_members[index].ty, field_indices)?;
 
                 TypeInner::Struct {
                     members: new_members,