monitordisk: lower inode check warning to note

Filesystems like btrfs and reiserfs sets the inode count to 0, since
they don't have an inode concept. This is expected, and having a warning
show up every time you run bitbake can cause undue concern.

Signed-off-by: Olof Johansson <olof.johansson@axis.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>