uprobes/x86: Kill the "autask" arg of riprel_pre_xol()

default_pre_xol_op() passes &current->utask->autask to riprel_pre_xol()
and this is just ugly because it still needs to load current->utask to
read ->vaddr.

Remove this argument, change riprel_pre_xol() to use current->utask.

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