ocxl: Change return type for fault handler

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.

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

There is an existing bug when vm_insert_pfn() can return ENOMEM which
was ignored and VM_FAULT_NOPAGE returned as default. The new inline
vmf_insert_pfn() has removed this inefficiency by returning correct
vm_fault_ type.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Acked-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>