target-ppc: fix cpu_clone_regs

We only need to make sure that the clone syscall looks like it
succeeded, not clobber 60% of the register set.
Signed-off-by: NNathan Froyd <froydnj@codesourcery.com>
Signed-off-by: Nmalc <av1474@comtv.ru>

target-ppc/cpu.h

@@ -817,11 +817,9 @@ static inline int cpu_mmu_index (CPUState *env)
 #if defined(CONFIG_USER_ONLY)
 static inline void cpu_clone_regs(CPUState *env, target_ulong newsp)
 {
-    int i;
     if (newsp)
         env->gpr[1] = newsp;
-    for (i = 7; i < 32; i++)
-        env->gpr[i] = 0;
+    env->gpr[3] = 0;
 }
 #endif