uio: Change return type to vm_fault_t

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 inst
ances are converted, vm_fault_t will become a di
stinct type.

Reference - 1c8f4220

 ("mm: change return type
to vm_fault_t")

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>