Zero memory in dma_alloc.

virtio-drivers now documents that this is required.

Bug: 274732281
Test: atest vmbase_example.integration_test
Change-Id: Ie3782e261cac130dd8f7d0c5905d90161789e76b
diff --git a/vmbase/example/src/pci.rs b/vmbase/example/src/pci.rs
index 41a3ff4..384a9c1 100644
--- a/vmbase/example/src/pci.rs
+++ b/vmbase/example/src/pci.rs
@@ -15,7 +15,7 @@
 //! Functions to scan the PCI bus for VirtIO device.
 
 use aarch64_paging::paging::MemoryRegion;
-use alloc::alloc::{alloc, dealloc, handle_alloc_error, Layout};
+use alloc::alloc::{alloc_zeroed, dealloc, handle_alloc_error, Layout};
 use core::{mem::size_of, ptr::NonNull};
 use fdtpci::PciInfo;
 use log::{debug, info};
@@ -103,7 +103,7 @@
         debug!("dma_alloc: pages={}", pages);
         let layout = Layout::from_size_align(pages * PAGE_SIZE, PAGE_SIZE).unwrap();
         // Safe because the layout has a non-zero size.
-        let vaddr = unsafe { alloc(layout) };
+        let vaddr = unsafe { alloc_zeroed(layout) };
         let vaddr =
             if let Some(vaddr) = NonNull::new(vaddr) { vaddr } else { handle_alloc_error(layout) };
         let paddr = virt_to_phys(vaddr);