Description of problem:
When oprofile doesn't support struct oprofile_operations method backtrace,
opcontrol --start-daemon prints a bogus error message.

This happens with Xenoprof (bug 401361).  Since that's unlikely to be fixed in
5.2, opcontrol needs to be fixed instead.

How reproducible:
Always.

Steps to Reproduce:
1. In a Xen dom0: opcontrol --start-daemon --no-vmlinux --xen=none
  
Actual results:
opcontrol prints:
/usr/bin/opcontrol: line 1082: echo: write error: Invalid argument
Using default event: CPU_CLK_UNHALTED:100000:0:1:1
Using 2.6+ OProfile kernel interface.
Using log file /var/lib/oprofile/oprofiled.log
Daemon started.

Expected results:
No write error.