rust: enable clippy::ptr_cast_constness

Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/qemu-api/src/cell.rs

@@ -1016,7 +1016,7 @@ impl<T> Opaque<T> {
 
     /// Returns a raw pointer to the opaque data.
     pub const fn as_ptr(&self) -> *const T {
-        self.as_mut_ptr() as *const _
+        self.as_mut_ptr().cast_const()
     }
 
     /// Returns a raw pointer to the opaque data that can be passed to a

rust/qemu-api/src/chardev.rs

@@ -160,7 +160,7 @@ impl CharBackend {
                 receive_cb,
                 event_cb,
                 None,
-                (owner as *const T as *mut T).cast::<c_void>(),
+                (owner as *const T).cast_mut().cast::<c_void>(),
                 core::ptr::null_mut(),
                 true,
             );

rust/qemu-api/src/qom.rs

@@ -388,7 +388,7 @@ where
     {
         #[allow(clippy::as_ptr_cast_mut)]
         {
-            self.as_ptr::<U>() as *mut _
+            self.as_ptr::<U>().cast_mut()
         }
     }
 }
@@ -638,7 +638,7 @@ impl<T: ObjectType> Owned<T> {
         // SAFETY NOTE: while NonNull requires a mutable pointer, only
         // Deref is implemented so the pointer passed to from_raw
         // remains const
-        Owned(NonNull::new(ptr as *mut T).unwrap())
+        Owned(NonNull::new(ptr.cast_mut()).unwrap())
     }
 
     /// Obtain a raw C pointer from a reference.  `src` is consumed

rust/qemu-api/src/timer.rs

@@ -81,7 +81,7 @@ impl Timer {
                 scale as c_int,
                 attributes as c_int,
                 Some(timer_cb),
-                (opaque as *const T).cast::<c_void>() as *mut c_void,
+                (opaque as *const T).cast::<c_void>().cast_mut(),
             )
         }
     }