Use new return type vm_fault_t for fault handler in struct
vm_operations_struct.  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")
Signed-off-by: NSouptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: NMatthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>