x86_64: pci-gart_64.c iommu_fullflush should be static

Impact: cleanup, reduce kernel size a bit, avoid sparse warning

Fixes sparse warning:

  arch/x86/kernel/pci-gart_64.c:55:5: warning: symbol 'iommu_fullflush' was not declared. Should it be static?
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/pci-gart_64.c

@@ -52,7 +52,7 @@ static u32 *iommu_gatt_base;		/* Remapping table */
  * to trigger bugs with some popular PCI cards, in particular 3ware (but
  * has been also also seen with Qlogic at least).
  */
-int iommu_fullflush = 1;
+static int iommu_fullflush = 1;
 
 /* Allocation bitmap for the remapping area: */
 static DEFINE_SPINLOCK(iommu_bitmap_lock);