Fix filesystem corruption

LittleFS bindings reported too big lookahead cache size which resulted
in corrupting adjacent structures (read and prog buffer), which in turn
resulted in filesystem corruption either by reallocating an already
allocated causing cycle or by corrupting data before writing it to disk.

src/fs.rs

@@ -61,7 +61,7 @@ impl<Storage: driver::Storage> Allocation<Storage> {
         let block_size: u32 = Storage::BLOCK_SIZE as _;
         let cache_size: u32 = <Storage as driver::Storage>::CACHE_SIZE::U32;
         let lookahead_size: u32 =
-            32 * <Storage as driver::Storage>::LOOKAHEADWORDS_SIZE::U32;
+            4 * <Storage as driver::Storage>::LOOKAHEADWORDS_SIZE::U32;
         let block_cycles: i32 = Storage::BLOCK_CYCLES as _;
         let block_count: u32 = Storage::BLOCK_COUNT as _;