Try to convince covscan that sysfs_read_file() doesn't leak on error.

Try to convince covscan that sysfs_read_file() doesn't leak on error.

Basically, covscan gets confused about some of our return paths and
doesn't  think the error condition correlates with not having allocated
(or having freed) the ram we're using to pass the file data back.

Signed-off-by: Peter Jones <pjones@redhat.com>