iommu: smar: Fix return value check of create_irq()

ia64 returns a negative error code when allocation fails andx86
returns 0. Make it handle both.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: x86@kernel.org
Acked-by: Joerg Roedel <joro@8bytes.org>
Cc: linux-ia64@vger.kernel.org
Cc: iommu@lists.linux-foundation.org
Link: http://lkml.kernel.org/r/20140507154336.178850165@linutronix.de


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>