hfsplus: do not cache and write next_alloc

We never look at it, nor change the next_alloc field in the superblock.  So
don't bother caching it or writing it out in hfsplus_sync_fs.

Signed-off-by: Christoph Hellwig <hch@tuxera.com>

fs/hfsplus/hfsplus_fs.h

@@ -129,7 +129,6 @@ struct hfsplus_sb_info {
 	int alloc_blksz_shift;
 	u32 total_blocks;
 	u32 free_blocks;
-	u32 next_alloc;
 	u32 next_cnid;
 	u32 file_count;
 	u32 folder_count;