vmm: Fix the memory slot index

The memory slot index provided to the DeviceManager was wrong since
only the RAM memory regions are set as user memory regions to KVM.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/vm.rs

@@ -1400,7 +1400,7 @@ impl<'a> Vm<'a> {
             &config,
             msi_capable,
             userspace_ioapic,
-            arch_mem_regions.len() as u32,
+            ram_regions.len() as u32,
         )
         .map_err(Error::DeviceManager)?;