ceph: adding new return type vm_fault_t

Use new return type vm_fault_t for page_mkwrite
and fault handler.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>