nilfs2: do not pass sbi to functions which can get it from inode

This removes argument for passing nilfs_sb_info structure from
nilfs_set_file_dirty and nilfs_load_inode_block functions.  We can get
a pointer to the structure from inodes.

[Stephen Rothwell <sfr@canb.auug.org.au>: fix conflict with commit
 b74c79e9]

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>