virtio-devices: replace as <pointer> casts with safer alternatives

`as` casts can change mutability, which quickly leads to undefined
behavior.

Signed-off-by: Julian Schindel <mail@arctic-alpaca.de>

virtio-devices/src/vhost_user/blk.rs

@@ -233,7 +233,7 @@ impl VirtioDevice for Blk {
     fn write_config(&mut self, offset: u64, data: &[u8]) {
         // The "writeback" field is the only mutable field
         let writeback_offset =
-            (&self.config.writeback as *const _ as u64) - (&self.config as *const _ as u64);
+            (&raw const self.config.writeback as u64) - (&raw const self.config as u64);
         if offset != writeback_offset || data.len() != std::mem::size_of_val(&self.config.writeback)
         {
             error!(

virtio-devices/src/vhost_user/vu_common_ctrl.rs

@@ -687,7 +687,7 @@ impl VhostUserHandle {
             // SAFETY: region is of size len
             let bitmap: &[u64] = unsafe {
                 // Cast the pointer to u64
-                let ptr = region.as_ptr() as *const u64;
+                let ptr = region.as_ptr().cast();
                 std::slice::from_raw_parts(ptr, len)
             };
             Ok(MemoryRangeTable::from_dirty_bitmap(