btrfs: switch cached fs_info::csum_size from u16 to u32

The fs_info value is 32bit, switch also the local u16 variables. This
leads to a better assembly code generated due to movzwl.

This simple change will shave some bytes on x86_64 and release config:

   text    data     bss     dec     hex filename
1090000   17980   14912 1122892  11224c pre/btrfs.ko
1089794   17980   14912 1122686  11217e post/btrfs.ko

DELTA: -206

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 1fe5961..f3f666b 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -336,7 +336,7 @@ static int check_csum_item(struct extent_buffer *leaf, struct btrfs_key *key,
 {
 	struct btrfs_fs_info *fs_info = leaf->fs_info;
 	u32 sectorsize = fs_info->sectorsize;
-	const u16 csumsize = fs_info->csum_size;
+	const u32 csumsize = fs_info->csum_size;
 
 	if (key->objectid != BTRFS_EXTENT_CSUM_OBJECTID) {
 		generic_err(leaf, slot,