fs: littlefs: Fix lookahead buffer sizing

The lookahead buffer is a bitmap containing info on free blocks and does
not have a minimum size or an alignment requirement.

This fixes the arbitrary 4 * block_size requirement for block devices
and fixes Kconfig documentation to remove a reference to nonexistent
8 byte alignment requirement.

Signed-off-by: Djordje Nedic <nedic.djordje2@gmail.com>

subsys/fs/Kconfig.littlefs

@@ -56,8 +56,7 @@ config FS_LITTLEFS_LOOKAHEAD_SIZE
 	help
 	  A larger lookahead buffer increases the number of blocks found
 	  during an allocation pass. The lookahead buffer is stored as a
-	  compact bitmap, so each byte of RAM can track 8 blocks. Must
-	  be a multiple of 8.
+	  compact bitmap, so each byte of RAM can track 8 blocks.
 
 config FS_LITTLEFS_BLOCK_CYCLES
 	int "Number of erase cycles before moving data to another block"

subsys/fs/littlefs_fs.c

@@ -844,8 +844,6 @@ static int littlefs_init_cfg(struct fs_littlefs *fs, int flags)
 	lcp->context = fs->backend;
 	/* Set the validated/defaulted values. */
 	if (littlefs_on_blkdev(flags)) {
-		lfs_size_t new_lookahead_size = block_size * 4;
-
 		lcp->read = lfs_api_read_blk;
 		lcp->prog = lfs_api_prog_blk;
 		lcp->erase = lfs_api_erase_blk;
@@ -859,12 +857,7 @@ static int littlefs_init_cfg(struct fs_littlefs *fs, int flags)
 		}
 		lcp->cache_size = ROUND_DOWN(cache_size, block_size);
 
-		if (lookahead_size < new_lookahead_size) {
-			LOG_ERR("Configured lookahead size is too small: %d < %d",
-				lookahead_size, new_lookahead_size);
-			return -ENOMEM;
-		}
-		lcp->lookahead_size = new_lookahead_size;
+		lcp->lookahead_size = lookahead_size;
 
 		lcp->sync = lfs_api_sync_blk;