[css-grid-3] Fix step number reference. w3c#9328

Author: tabatkins

css-grid-3/Overview.bs

@@ -1072,7 +1072,7 @@ Masonry Layout and Placement Algorithm</h3>
 					find the largest [=running position=] of the [=grid axis=] tracks
 					that the item would span if it were placed at this line,
 					and call this position <var>max_pos</var>.
-				<li>Increment the line number and repeat step 2
+				<li>Repeat the previous step for each successive line number
 					until the item would no longer fit inside the grid.
 				<li>Let |possible lines| be the line that resulted in the smallest <var>max_pos</var>,
 					and all lines that result in a <var>max_pos</var> within the [=tie threshold=] of this <var>max_pos</var>.