x86/microcode/intel: Drop orig_sum from ext signature checksum

It is 0 because for !0 values we would have exited already.

Signed-off-by: Borislav Petkov <bp@suse.de>
Link: http://lkml.kernel.org/r/1457345404-28884-6-git-send-email-bp@alien8.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>