Changed rbyd.weight to unsigned

This should really be unsigned, rbyd weights can not be negative.

Note this is different than data.size, etc, since the signedness there
is used to differentiate the underlying encoding. Accessing data.size
directly is usually an error, though we do access it directly in several
places when assuming the underlying encoding. Signedness warnings are
actually a good thing in that case.

lfs.h

@@ -337,9 +337,9 @@ typedef struct lfs_cache {
 
 // TODO do we get ram savings with a lfsr_rorbyd_t substruct? need to measure
 typedef struct lfsr_rbyd {
-    // note this lines up with weight in lfsr_btree_t
+    // note this lines up with weight in lfsr_data_t
     // sign(weight)=0 => rbyd
-    lfsr_srid_t weight;
+    lfsr_rid_t weight;
     lfs_block_t blocks[2];
     // sign(trunk)=0    => normal rbyd
     // sign(trunk)=1    => shrub rbyd
@@ -482,7 +482,6 @@ typedef struct lfs_file {
 } lfs_file_t;
 
 typedef struct lfsr_bptr {
-    // note data.size lines up with weight in lfsr_btree_t
     lfsr_data_t data;
     lfs_size_t cksize;
     uint32_t cksum;