thp: consolidate assert checks in __split_huge_page()

It doesn't make sense to have two assert checks for each invariant: one
for printing and one for BUG().

Let's trigger BUG() if we print error message.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/huge_memory.c

@@ -1830,10 +1830,11 @@ static void __split_huge_page(struct page *page,
 	 * the newly established pmd of the child later during the
 	 * walk, to be able to set it as pmd_trans_splitting too.
 	 */
-	if (mapcount != page_mapcount(page))
+	if (mapcount != page_mapcount(page)) {
 		printk(KERN_ERR "mapcount %d page_mapcount %d\n",
 		       mapcount, page_mapcount(page));
-	BUG_ON(mapcount != page_mapcount(page));
+		BUG();
+	}
 
 	__split_huge_page_refcount(page, list);
 
@@ -1844,10 +1845,11 @@ static void __split_huge_page(struct page *page,
 		BUG_ON(is_vma_temporary_stack(vma));
 		mapcount2 += __split_huge_page_map(page, vma, addr);
 	}
-	if (mapcount != mapcount2)
+	if (mapcount != mapcount2) {
 		printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",
 		       mapcount, mapcount2, page_mapcount(page));
-	BUG_ON(mapcount != mapcount2);
+		BUG();
+	}
 }
 
 /*