uprobes/x86: Kill the "ia32_compat" check in handle_riprel_insn(), remove "mm" arg
Kill the "mm->context.ia32_compat" check in handle_riprel_insn(), if
it is true insn_rip_relative() must return false. validate_insn_bits()
passed "ia32_compat" as !x86_64 to insn_init(), and insn_rip_relative()
checks insn->x86_64.
Also, remove the no longer needed "struct mm_struct *mm" argument and
the unnecessary "return" at the end.