efi: Fix a mistype in comments mentioning efivar_entry_iter_begin()

Signed-off-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200305084041.24053-4-vdronov@redhat.com
Link: https://lore.kernel.org/r/20200308080859.21568-26-ardb@kernel.org