bitbake: monitordisk.py: disable inode checking for btrfs

The btrfs doesn't have static inode, so disable the inode check for it,
the previouse patch has set it:

minInode = None

But this is incorrect, the minInode is just a temporary variable, it
should be:

self.devDict[k][2] = None

[YOCTO #3609]

(Bitbake rev: 7e45149c292bc92314af9b42962fde8f603a179f)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/monitordisk.py

@@ -244,7 +244,7 @@ class diskMonitor:
                     # checking for such a fs.
                     if st.f_files == 0:
                         logger.warn("Inode check for %s is unavaliable, will remove it from disk monitor" % path)
-                        minInode = None
+                        self.devDict[k][2] = None
                         continue
                     # Always show warning, the self.checked would always be False if the action is WARN
                     if self.preFreeI[k] == 0 or self.preFreeI[k] - freeInode > self.inodeInterval and not self.checked[k]: