fix vortex-gpu compilation (#5315)

I started to see vortex-gpu compilation issues after running `cargo
clean`, this fixed the compilation for me

Signed-off-by: Onur Satici <onur@spiraldb.com>

Author: onursatici

vortex-gpu/src/gpu_array.rs

@@ -117,7 +117,7 @@ impl GpuPrimitiveVector {
             let mut buffer = BufferMut::<P>::with_capacity(self.len);
             unsafe { buffer.set_len(self.len) }
             stream
-                .memcpy_dtoh(&self.as_slice::<P>(), &mut buffer)
+                .memcpy_dtoh(&self.as_slice::<P>(), &mut buffer[..])
                 .map_err(|e| vortex_err!("Failed to copy to device: {e}"))?;
             stream
                 .synchronize()

vortex-gpu/src/take.rs

@@ -114,7 +114,7 @@ where
     unsafe { buffer.set_len(codes.len()) }
 
     stream
-        .memcpy_dtoh(&cu_out, &mut buffer)
+        .memcpy_dtoh(&cu_out, &mut buffer[..])
         .map_err(|e| vortex_err!("Failed to copy to device: {e}"))?;
     stream
         .synchronize()