s390/jump_label: Use %*ph to print small buffers

printk() supports %*ph format specifier for printing a small buffers,
let's use it intead of %02x %02x...

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>