Apply suggestions from code review

Co-authored-by: Ralf Jung <post@ralfj.de>

Author: WaffleLapkin

compiler/rustc_const_eval/src/interpret/place.rs

@@ -443,8 +443,8 @@ where
     /// `align` information is lost!
     /// This is the inverse of `imm_ptr_to_mplace`.
     ///
-    /// If `ptr_ty` is provided the resulting pointer will be of that type (instead of `*mut _`).
-    /// `ptr_ty` must be a type with builtin deref which derefs to the type of `mplace` (`mplace.layout.ty`)
+    /// If `ptr_ty` is provided, the resulting pointer will be of that type. Otherwise, it defaults to `*mut _`.
+    /// `ptr_ty` must be a type with builtin deref which derefs to the type of `mplace` (`mplace.layout.ty`).
     pub fn mplace_to_imm_ptr(
         &self,
         mplace: &MPlaceTy<'tcx, M::Provenance>,
@@ -454,7 +454,7 @@ where
 
         let ptr_ty = ptr_ty
             .inspect(|t| assert_eq!(t.builtin_deref(true), Some(mplace.layout.ty)))
-            .unwrap_or(Ty::new_mut_ptr(self.tcx.tcx, mplace.layout.ty));
+            .unwrap_or_else(|| Ty::new_mut_ptr(self.tcx.tcx, mplace.layout.ty));
 
         let layout = self.layout_of(ptr_ty)?;
         interp_ok(ImmTy::from_immediate(imm, layout))