dmar: fix dmar_parse_dev() devices_cnt error condition check

It is possible that,
instead of PCI endpoint/sub-hierarchy structures, only IO-APIC/HPET
devices may be reported under device scope structures. Fix the devices_cnt
error check, which cares about only PCI structures and removes the
dma-remapping unit structure (dmaru) when the devices_cnt is zero
and include_all flag is not set.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Acked-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>