[IA64] export sn_dma_mapping_error for libata

Signed-off-by: Patrick Gefre <pfg@sgi.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/sn/pci/pci_dma.c

@@ -474,3 +474,4 @@ EXPORT_SYMBOL(sn_pci_unmap_sg);
 EXPORT_SYMBOL(sn_pci_alloc_consistent);
 EXPORT_SYMBOL(sn_pci_free_consistent);
 EXPORT_SYMBOL(sn_pci_dma_supported);
+EXPORT_SYMBOL(sn_dma_mapping_error);