f2fs: Get the superblock from the mapping instead of the page

It's slightly more efficient to go directly from the mapping to the
superblock than to go from the page.  Now that these routines have
the mapping passed to them, there's no reason not to use it.
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>

fs/f2fs/checkpoint.c

@@ -456,7 +456,7 @@ static bool f2fs_dirty_meta_folio(struct address_space *mapping,
 		folio_mark_uptodate(folio);
 	if (!folio_test_dirty(folio)) {
 		filemap_dirty_folio(mapping, folio);
-		inc_page_count(F2FS_P_SB(&folio->page), F2FS_DIRTY_META);
+		inc_page_count(F2FS_M_SB(mapping), F2FS_DIRTY_META);
 		set_page_private_reference(&folio->page);
 		return true;
 	}

fs/f2fs/node.c

@@ -2146,11 +2146,11 @@ static bool f2fs_dirty_node_folio(struct address_space *mapping,
 		folio_mark_uptodate(folio);
 #ifdef CONFIG_F2FS_CHECK_FS
 	if (IS_INODE(&folio->page))
-		f2fs_inode_chksum_set(F2FS_P_SB(&folio->page), &folio->page);
+		f2fs_inode_chksum_set(F2FS_M_SB(mapping), &folio->page);
 #endif
 	if (!folio_test_dirty(folio)) {
 		filemap_dirty_folio(mapping, folio);
-		inc_page_count(F2FS_P_SB(&folio->page), F2FS_DIRTY_NODES);
+		inc_page_count(F2FS_M_SB(mapping), F2FS_DIRTY_NODES);
 		set_page_private_reference(&folio->page);
 		return true;
 	}