usb: mon: Change return type to vm_fault_t

Use new return type vm_fault_t for the 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.

Reference id -> 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>