iocost: Fix iocost_monitor.py due to helper type mismatch

iocost_monitor.py broke with recent versions of drgn due to helper
being stricter about types.  Fix it so that it uses the correct type.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Omar Sandoval <osandov@fb.com>
1 file changed