For whatever reasons this can happen. For real testcases the test will
notice the -EIO and fall over, but we also have some testcases that
just read all debugfs files. And that shouldn't cause dmesg spam.

So tune it down a bit so that we still have the information for
debugging. And change the errno so that real testcases can easily
differentiate.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=84890Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>