mm/interval_tree: add comments to improve code readability

Add a comment explaining the value of the ISSTATIC parameter, Inform the
reader that this is not a coding style issue.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Zhiyuan Dai <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/interval_tree.c

···
 
 INTERVAL_TREE_DEFINE(struct vm_area_struct, shared.rb,
 		     unsigned long, shared.rb_subtree_last,
-		     vma_start_pgoff, vma_last_pgoff,, vma_interval_tree)
+		     vma_start_pgoff, vma_last_pgoff, /* empty */, vma_interval_tree)
 
 /* Insert node immediately after prev in the interval tree */
 void vma_interval_tree_insert_after(struct vm_area_struct *node,