rust: iommu: replace core::mem::zeroed with Zeroable::zeroed

All types in `bindings` implement `Zeroable` if they can. This enables
using `Zeroable::zeroed` for `io_pgtable_cfg` initialization instead
of relying on `..unsafe { core::mem::zeroed() }`.

This change improves readability and removes an unnecessary unsafe
block.

Link: https://github.com/Rust-for-Linux/linux/issues/1189
Suggested-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Nicolás Antinori <nico.antinori.7@gmail.com>
Acked-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

rust/kernel/iommu/pgtable.rs

@@ -102,8 +102,7 @@ impl<F: IoPageTableFmt> IoPageTable<F> {
             coherent_walk: config.coherent_walk,
             tlb: &raw const NOOP_FLUSH_OPS,
             iommu_dev: dev.as_raw(),
-            // SAFETY: All zeroes is a valid value for `struct io_pgtable_cfg`.
-            ..unsafe { core::mem::zeroed() }
+            ..Zeroable::zeroed()
         };
 
         // SAFETY: