ipc: use new return type 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/20180425043413.GA21467@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>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Cc: Manfred Spraul <manfred@colorfullife.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ipc/shm.c

@@ -408,7 +408,7 @@ void exit_shm(struct task_struct *task)
 	up_write(&shm_ids(ns).rwsem);
 }
 
-static int shm_fault(struct vm_fault *vmf)
+static vm_fault_t shm_fault(struct vm_fault *vmf)
 {
 	struct file *file = vmf->vma->vm_file;
 	struct shm_file_data *sfd = shm_file_data(file);