uprobes/tracing: Make seq_printf() code uretprobe-friendly

Change probes_seq_show() and print_uprobe_event() to check
is_ret_probe() and print the correct data.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: Anton Arapov <anton@redhat.com>