arch: return the correct size for SMBIOS occupied space

The original value didn't include the size of the entry point structure.

The caused the last entry to be corrupted by other code.

Signed-off-by: Wei Liu <liuwe@microsoft.com>

arch/src/x86_64/smbios.rs

@@ -250,7 +250,7 @@ pub fn setup_smbios(
             .map_err(|_| Error::WriteSmbiosEp)?;
     }
 
-    Ok(curptr.unchecked_offset_from(physptr))
+    Ok(curptr.unchecked_offset_from(physptr) + std::mem::size_of::<Smbios30Entrypoint>() as u64)
 }
 
 #[cfg(test)]