boot-qemu.py: Fix '--efi' for x86_64

Pretty obvious typo...

Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: nathanchance

boot-qemu.py

@@ -699,8 +699,8 @@ def run(self):
                 Path('OVMF/OVMF_VARS.fd'),  # Debian and Ubuntu
             ]
             ovmf_vars = utils.find_first_file(usr_share, ovmf_vars_locations)
-            self._efi_vars = Path(utils.BOOT_UTILS, 'images', self.initrd_arch,
-                                  ovmf_vars.name)
+            self._efi_vars = Path(utils.BOOT_UTILS, 'images',
+                                  self._initrd_arch, ovmf_vars.name)
             # This file is in /usr/share, so it must be copied in order to be
             # modified.
             shutil.copyfile(ovmf_vars, self._efi_vars)