mm/mmap.c: replace do_brk with do_brk_flags in comment of insert_vm_struct()

Replace do_brk with do_brk_flags in comment of insert_vm_struct(), since
do_brk was removed in following commit.

Fixes: bb177a73 ("mm: do not bug_on on incorrect length in __mm_populate()")
Signed-off-by: Liao Pingfang <liao.pingfang@zte.com.cn>
Signed-off-by: Yi Wang <wang.yi59@zte.com.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/1600650778-43230-1-git-send-email-wang.yi59@zte.com.cnSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -3233,7 +3233,7 @@ int insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vma)
 	 * By setting it to reflect the virtual start address of the
 	 * vma, merges and splits can happen in a seamless way, just
 	 * using the existing file pgoff checks and manipulations.
-	 * Similarly in do_mmap and in do_brk.
+	 * Similarly in do_mmap and in do_brk_flags.
 	 */
 	if (vma_is_anonymous(vma)) {
 		BUG_ON(vma->anon_vma);