Fix opencl interop examples to use OpenCL backend always

Author: 9prady9

opencl-interop/examples/custom_kernel.rs

@@ -7,6 +7,10 @@ use ocl_core::{ArgVal, Event};
 use std::ffi::CString;
 
 fn main() {
+    // Set the arrayfire backend to use OpenCL first,
+    // because CUDA is the automatically preferred if available
+    af::set_backend(af::Backend::OPENCL);
+
     af::info();
     let dims = af::dim4!(8);
     let af_buffer = af::constant(0f32, dims.clone());

opencl-interop/examples/ocl_af_app.rs

@@ -5,7 +5,8 @@ use arrayfire as af;
 use ocl_core::{ContextProperties, Event};
 
 fn main() {
-    // Set the arrayfire backend to use OopenCL first, because CUDA is the default
+    // Set the arrayfire backend to use OpenCL first,
+    // because CUDA is the automatically preferred if available
     af::set_backend(af::Backend::OPENCL);
 
     // Choose platform & device(s) to use. Create a context, queue,