mm/hmm: convert to use vm_fault_t

Convert to use vm_fault_t type as return type for fault handler.

kbuild reported warning during testing of
*mm-create-the-new-vm_fault_t-type.patch* available in below link -
https://patchwork.kernel.org/patch/10752741/

  kernel/memremap.c:46:34: warning: incorrect type in return expression
                           (different base types)
  kernel/memremap.c:46:34: expected restricted vm_fault_t
  kernel/memremap.c:46:34: got int

This patch has fixed the warnings and also hmm_devmem_fault() is
converted to return vm_fault_t to avoid further warnings.

[sfr@canb.auug.org.au: drm/nouveau/dmem: update for struct hmm_devmem_ops member change]
  Link: http://lkml.kernel.org/r/20190220174407.753d94e5@canb.auug.org.au
Link: http://lkml.kernel.org/r/20190110145900.GA1317@jordon-HP-15-Notebook-PCSigned-off-by: NSouptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: NJérôme Glisse <jglisse@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/nouveau/nouveau_dmem.c

@@ -261,7 +261,7 @@ static const struct migrate_vma_ops nouveau_dmem_fault_migrate_ops = {
 	.finalize_and_map	= nouveau_dmem_fault_finalize_and_map,
 };
 
-static int
+static vm_fault_t
 nouveau_dmem_fault(struct hmm_devmem *devmem,
 		   struct vm_area_struct *vma,
 		   unsigned long addr,

include/linux/hmm.h

@@ -468,7 +468,7 @@ struct hmm_devmem_ops {
 	 * Note that mmap semaphore is held in read mode at least when this
 	 * callback occurs, hence the vma is valid upon callback entry.
 	 */
-	int (*fault)(struct hmm_devmem *devmem,
+	vm_fault_t (*fault)(struct hmm_devmem *devmem,
 		     struct vm_area_struct *vma,
 		     unsigned long addr,
 		     const struct page *page,
@@ -511,7 +511,7 @@ struct hmm_devmem_ops {
  * chunk, as an optimization. It must, however, prioritize the faulting address
  * over all the others.
  */
-typedef int (*dev_page_fault_t)(struct vm_area_struct *vma,
+typedef vm_fault_t (*dev_page_fault_t)(struct vm_area_struct *vma,
 				unsigned long addr,
 				const struct page *page,
 				unsigned int flags,

mm/hmm.c

@@ -990,7 +990,7 @@ static void hmm_devmem_ref_kill(struct percpu_ref *ref)
 	percpu_ref_kill(ref);
 }
 
-static int hmm_devmem_fault(struct vm_area_struct *vma,
+static vm_fault_t hmm_devmem_fault(struct vm_area_struct *vma,
 			    unsigned long addr,
 			    const struct page *page,
 			    unsigned int flags,