gpu: drm: qxl: Adding new typedef vm_fault_t

gpu: drm: qxl: Adding new typedef vm_fault_t

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.

Reference id -> cbb1cb712168 ("mm: change return type to
vm_fault_t")

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20180417133844.GA30256@jordon-HP-15-Notebook-PC
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>