rust: acpi: remove unneeded cast to clean future Clippy warning

A future Clippy warning, `clippy::as_underscore`, is getting enabled in
parallel in the rust-next tree:

    error: using `as _` conversion
      --> rust/kernel/acpi.rs:25:9
       |
    25 |         self.0.driver_data as _
       |         ^^^^^^^^^^^^^^^^^^^^^^-
       |                               |
       |                               help: consider giving the type explicitly: `usize`

The type is already `ulong`, which nowadays is always `usize`, so the
cast is unneeded. Thus remove it, which in turn will avoid the warning
in the future.

Other abstractions of device tables do not use a cast here either.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Reviewed-by: Trevor Gross <tmgross@umich.edu>
Link: https://lore.kernel.org/r/20250701174656.62205-1-ojeda@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

rust/kernel/acpi.rs

@@ -22,7 +22,7 @@ unsafe impl RawDeviceId for DeviceId {
     const DRIVER_DATA_OFFSET: usize = core::mem::offset_of!(bindings::acpi_device_id, driver_data);
 
     fn index(&self) -> usize {
-        self.0.driver_data as _
+        self.0.driver_data
     }
 }