vmbase_example: Use layout::crosvm for MMIO range

Use the constants, which have the same values.

Test: TH
Change-Id: I9eda16ba892348dd2a241f45cce50bc6e8de3c9a
diff --git a/guest/vmbase_example/src/layout.rs b/guest/vmbase_example/src/layout.rs
index 50ecb7e..55c7283 100644
--- a/guest/vmbase_example/src/layout.rs
+++ b/guest/vmbase_example/src/layout.rs
@@ -19,8 +19,8 @@
 use log::info;
 use vmbase::{layout, memory::PAGE_SIZE};
 
-/// The first 1 GiB of memory are used for MMIO.
-pub const DEVICE_REGION: MemoryRegion = MemoryRegion::new(0, 0x40000000);
+pub const DEVICE_REGION: MemoryRegion =
+    MemoryRegion::new(layout::crosvm::MMIO_START, layout::crosvm::MMIO_END);
 
 /// Writable data region for the stack.
 pub fn boot_stack_range() -> Range<VirtualAddress> {