nilfs2: Convert nilfs_btnode_submit_block to bh_submit()

nilfs2: Convert nilfs_btnode_submit_block to bh_submit()

Avoid an extra indirect function call and changing the buffer refcount
by using bh_submit() instead of submit_bh().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20260528173150.1093780-28-willy@infradead.org
Acked-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: linux-nilfs@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>