[IA64] remove duplicated #include from pci-dma.c

Removed duplicated #include <asm/machvec.h> and <linux/string.h> in
arch/ia64/kernel/pci-dma.c.
Signed-off-by: Huang Weiyi <weiyi.huang@gmail.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/pci-dma.c

@@ -12,13 +12,11 @@
 #include <asm/machvec.h>
 #include <linux/dma-mapping.h>
 
-#include <asm/machvec.h>
 #include <asm/system.h>
 
 #ifdef CONFIG_DMAR
 
 #include <linux/kernel.h>
-#include <linux/string.h>
 
 #include <asm/page.h>
 #include <asm/iommu.h>