sparc64: fix ptrace interaction with force_successful_syscall_return()

we want syscall_trace_leave() called on exit from any syscall;
skipping its call in case we'd done force_successful_syscall_return()
is broken...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>