x86, mm: Use max_pfn instead of highend_pfn

The 'highend_pfn' variable is always set to 'max_pfn' so just
use the latter directly.

Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
Link: http://lkml.kernel.org/r/1320155902-10424-3-git-send-email-penberg@kernel.org


Signed-off-by: Ingo Molnar <mingo@elte.hu>