[IA64] Fix spinaphore down_spin()

Typo in down_spin() meant it only read the low 32 bits of the
"serve" value, instead of the full 64 bits. This results in the
system hanging when the values in ticket/serve get larger than
32-bits. A big enough system running the right test can hit this
in a just a few hours.

Broken since 883a3acf5b0d4782ac35981227a0d094e8b44850
    [IA64] Re-implement spinaphores using ticket lock concepts

Reported via IRC by Bjorn Helgaas

Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/mm/tlb.c

@@ -121,7 +121,7 @@ static inline void down_spin(struct spinaphore *ss)
 	ia64_invala();
 
 	for (;;) {
-		asm volatile ("ld4.c.nc %0=[%1]" : "=r"(serve) : "r"(&ss->serve) : "memory");
+		asm volatile ("ld8.c.nc %0=[%1]" : "=r"(serve) : "r"(&ss->serve) : "memory");
 		if (time_before(t, serve))
 			return;
 		cpu_relax();