virtio: kumquat: slice length fix

Causes issues with some versions of host gfxstream.

Reviewed-by: David Gilhooley <djgilhooley.gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37855>

src/virtio/virtgpu_kumquat/virtgpu_kumquat.rs

@@ -154,7 +154,7 @@ impl VirtGpuKumquat {
     pub fn get_caps(&self, capset_id: u32, slice: &mut [u8]) -> MesaResult<()> {
         let caps = self.capsets.get(&capset_id).ok_or(MesaError::Unsupported)?;
         let length = min(slice.len(), caps.len());
-        slice.copy_from_slice(&caps[0..length]);
+        slice[0..length].copy_from_slice(&caps[0..length]);
         Ok(())
     }