Arm backend: Fix Ethos-U handle release on platform_init() failure (pytorch#22897)

### Problem

pytorch#22531 removed dynamic allocation but platform_init() failure still
calls `delete`.

### Change

Release the handle with the destructor `handle->~ExecutionHandle()` to
follow up on pytorch#22531.

Signed-off-by: Youngsik Yang <vacu9708@gmail.com>

Author: vacu9708

backends/arm/runtime/EthosUBackend.cpp

@@ -146,7 +146,7 @@ class EthosUBackend final : public ::executorch::runtime::BackendInterface {
     const Error platform_status =
         platform_init(compile_specs, allocator, handle);
     if (platform_status != Error::Ok) {
-      delete handle;
+      handle->~ExecutionHandle();
       return platform_status;
     }