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")

Previously vm_insert_pfn() returns err which driver mapped into
VM_FAULT_* type. The new function vmf_insert_pfn() will replace this
inefficiency by returning VM_FAULT_* type.
Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>