entaviv/isa: Silence warnings about non snake case names

These are benign style warnings. The code is generated by bindgen and it's a bug there that these
names get generated at all.

Silences these warnings since we can't do anything about them:

```
warning: method `use__raw` should have a snake case name
   --> src/etnaviv/isa/isa_bindings.rs:358:19
    |
358 |     pub unsafe fn use__raw(this: *const Self) -> ::std::os::raw::c_uint {
    |                   ^^^^^^^^ help: convert the identifier to snake case: `use_raw`
    |
    = note: `#[warn(non_snake_case)]` on by default

warning: method `use__raw` should have a snake case name
    --> src/etnaviv/isa/isa_bindings.rs:1023:19
     |
1023 |     pub unsafe fn use__raw(this: *const Self) -> ::std::os::raw::c_uint {
     |                   ^^^^^^^^ help: convert the identifier to snake case: `use_raw`
```

Fixes: 15a784689e ("etnaviv: isa: Generate Rust FFI bindings for asm.h")
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34969>

src/etnaviv/isa/meson.build

@@ -118,6 +118,7 @@ if with_tools.contains('etnaviv')
     rust_abi : 'rust',
     rust_args: [
       '-Anon_camel_case_types',
+      '-Anon_snake_case',
     ],
   )