x86/microcode: Mark microcode_id[] as __initconst

It's not being used for other than creating module aliases (i.e.
no loadable section has any reference to it).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/4FDF1EFD020000780008A65D@nat28.tlf.novell.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>