kernel/relay.c: change return type to vm_fault_t

Use new return type vm_fault_t for fault handler.  For now, this is just
documenting that the function returns a VM_FAULT value rather than an
errno.  Once all instances are converted, vm_fault_t will become a
distinct type.

commit 1c8f4220 ("mm: change return type to vm_fault_t")

Link: http://lkml.kernel.org/r/20180510140335.GA25363@jordon-HP-15-Notebook-PCSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/relay.c

@@ -39,7 +39,7 @@ static void relay_file_mmap_close(struct vm_area_struct *vma)
 /*
  * fault() vm_op implementation for relay file mapping.
  */
-static int relay_buf_fault(struct vm_fault *vmf)
+static vm_fault_t relay_buf_fault(struct vm_fault *vmf)
 {
 	struct page *page;
 	struct rchan_buf *buf = vmf->vma->vm_private_data;