make get_file() return its argument

simplifies a bunch of callers...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/mm/nommu.c b/mm/nommu.c
index d4b0c10..dee2ff8 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1282,10 +1282,8 @@
 	vma->vm_pgoff = pgoff;
 
 	if (file) {
-		region->vm_file = file;
-		get_file(file);
-		vma->vm_file = file;
-		get_file(file);
+		region->vm_file = get_file(file);
+		vma->vm_file = get_file(file);
 		if (vm_flags & VM_EXECUTABLE) {
 			added_exe_file_vma(current->mm);
 			vma->vm_mm = current->mm;