mm/memory.c: use NULL instead of literal 0

Patch fixes sparse warning: Using plain integer as NULL pointer.
Replaces assignment of 0 to pointer with NULL assignment.

Link: http://lkml.kernel.org/r/1485992240-10986-2-git-send-email-me@tobin.cc
Signed-off-by: Tobin C Harding <me@tobin.cc>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -2920,7 +2920,7 @@ static int pte_alloc_one_map(struct vm_fault *vmf)
 		atomic_long_inc(&vma->vm_mm->nr_ptes);
 		pmd_populate(vma->vm_mm, vmf->pmd, vmf->prealloc_pte);
 		spin_unlock(vmf->ptl);
-		vmf->prealloc_pte = 0;
+		vmf->prealloc_pte = NULL;
 	} else if (unlikely(pte_alloc(vma->vm_mm, vmf->pmd, vmf->address))) {
 		return VM_FAULT_OOM;
 	}
@@ -2968,7 +2968,7 @@ static void deposit_prealloc_pte(struct vm_fault *vmf)
 	 * count that as nr_ptes.
 	 */
 	atomic_long_inc(&vma->vm_mm->nr_ptes);
-	vmf->prealloc_pte = 0;
+	vmf->prealloc_pte = NULL;
 }
 
 static int do_set_pmd(struct vm_fault *vmf, struct page *page)
@@ -3374,7 +3374,7 @@ static int do_fault(struct vm_fault *vmf)
 	/* preallocated pagetable is unused: free it */
 	if (vmf->prealloc_pte) {
 		pte_free(vma->vm_mm, vmf->prealloc_pte);
-		vmf->prealloc_pte = 0;
+		vmf->prealloc_pte = NULL;
 	}
 	return ret;
 }