Security: remove security_file_mmap hook sparse-warnings (NULL as 0).

Fixing:
  CHECK   mm/mmap.c
mm/mmap.c:1623:29: warning: Using plain integer as NULL pointer
mm/mmap.c:1623:29: warning: Using plain integer as NULL pointer
mm/mmap.c:1944:29: warning: Using plain integer as NULL pointer
Signed-off-by: Richard Knutsson <ricknu-0@student.ltu.se>
Signed-off-by: James Morris <jmorris@namei.org>

mm/mmap.c

@@ -1620,7 +1620,7 @@ static inline int expand_downwards(struct vm_area_struct *vma,
 		return -ENOMEM;
 
 	address &= PAGE_MASK;
-	error = security_file_mmap(0, 0, 0, 0, address, 1);
+	error = security_file_mmap(NULL, 0, 0, 0, address, 1);
 	if (error)
 		return error;
 
@@ -1941,7 +1941,7 @@ unsigned long do_brk(unsigned long addr, unsigned long len)
 	if (is_hugepage_only_range(mm, addr, len))
 		return -EINVAL;
 
-	error = security_file_mmap(0, 0, 0, 0, addr, 1);
+	error = security_file_mmap(NULL, 0, 0, 0, addr, 1);
 	if (error)
 		return error;