Tweaked dbg script headers to match the mount info log

The main difference being rendering the weight with a single letter "w"
prefix:

  $ ./scripts/dbglfs.py disk -b4096
  littlefs v0.0 4096x256 0x{1,0}.8b w2.512, rev eb7f2a0d
  ...

This lets us add valuable weight info without too much noise.

Adopting this in the dbg scripts is nice for consistency.

scripts/dbgmtree.py

@@ -1500,10 +1500,10 @@ def main(disk, mroots=None, *,
         #### actual debugging begins here
 
         # print some information about the mtree
-        print('mtree %s, rev %08x, weight %d.%d, cksum %08x' % (
+        print('mtree %s w%d.%d, rev %08x, cksum %08x' % (
             mroot.addr(),
-            mroot.rev,
             bweight//mleaf_weight, 1*mleaf_weight,
+            mroot.rev,
             mroot.cksum))
 
         # dynamically size the id field