linux-user: Fix Stack Pointer Bug in PPC setup_rt_frame

The code that sets the stack frame back pointer is incorrect for
the setup_rt_frame() code; qemu will abort (SIGSEGV) in some
environments.  The setup_frame code  was fixed in commit
beb526b1 but the setup_rt_frame
code was not.

Make the setup_rt_frame code consistent with the setup_frame
code.
Signed-off-by: NTom Musta <tommusta@gmail.com>
Signed-off-by: NAlexander Graf <agraf@suse.de>

linux-user/signal.c

@@ -4751,7 +4751,7 @@ static void setup_rt_frame(int sig, struct target_sigaction *ka,
 
     /* Create a stack frame for the caller of the handler.  */
     newsp = rt_sf_addr - (SIGNAL_FRAMESIZE + 16);
-    __put_user(env->gpr[1], (target_ulong *)(uintptr_t) newsp);
+    err |= put_user(env->gpr[1], newsp, target_ulong);
 
     if (err)
         goto sigsegv;