x86: fix function definitions after: x86: apic - introduce imcr_ helpers

The patch "introduce imcr_ helpers" introduced good comments, but
also a few new compile warnings. This fixes the function definitions
to have a 'void' return type.

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
LKML-Reference: <20090413153924.GA20287@mailshack.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>