multiboot2: Fix EFI Memory Map 'last_area' calculation

Correct EFI 'last_area' calculation and align it to be more similar the E820 version.

(Previously, iterating the EFI Memory map resulted in a superfluous entry as it ran over the next tag)

Author: A0lson

multiboot2/src/memory_map.rs

@@ -140,7 +140,7 @@ impl EFIMemoryMapTag {
         let start_area = (&self.first_desc) as *const EFIMemoryDesc;
         EFIMemoryAreaIter {
             current_area: start_area as u64,
-            last_area: (self_ptr as u64 + self.size as u64),
+            last_area: (self_ptr as u64 + (self.size - self.desc_size) as u64),
             entry_size: self.desc_size,
             phantom: PhantomData,
         }