x86: code cleanups in arch/x86/kernel/pci-gart_64.c

code cleanups:

                                       errors   lines of code   errors/KLOC
 arch/x86/kernel/pci-gart_64.c            183             748         244.6
 arch/x86/kernel/pci-gart_64.c              0             790             0
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>