bios: fix use of undefined initrd_dir variable in get_vmlinuz_path

Use the intended linuz_dir instead of initrd_dir in the function
get_vmlinuz_path.

src/utils/bios.py

@@ -36,7 +36,7 @@ def get_vmlinuz_path(mountpoint):
             target_file = file
 
     if not target_file:
-        raise OgError(f'vmlinuz not found in {initrd_dir}')
+        raise OgError(f'vmlinuz not found in {linuz_dir}')
 
     return os.path.join(linuz_dir, target_file)