uprobes/x86: Shift "insn_complete" from branch_setup_xol_ops() to uprobe_init_insn()

Change uprobe_init_insn() to make insn_complete() == T, this makes
other insn_get_*() calls unnecessary.

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