x86: don't try to allocate from DMA zone at first

If we fail, we'll loop into the allocation again,
and then allocate in the DMA zone.

Signed-off-by: Glauber Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>