drm: drm_vm: Use fallthrough;

Convert /* fallthrough */ style comments to fallthrough;

Convert the various uses of fallthrough comments to fallthrough;

Done via script
Link: https://lore.kernel.org/lkml/b56602fcf79f849e733e7b521bb0e17895d390fa.1582230379.git.joe@perches.com/

And by hand:

This file has a fallthrough comment outside of an #ifdef block
that causes gcc to emit a warning if converted in-place.

So move the new fallthrough; inside the containing #ifdef/#endif too.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/398db73cdc8a584fd7f34f5013c04df13ba90f64.1584040050.git.joe@perches.com

drivers/gpu/drm/drm_vm.c

@@ -595,8 +595,8 @@ static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma)
 			vma->vm_ops = &drm_vm_ops;
 			break;
 		}
+		fallthrough;	/* to _DRM_FRAME_BUFFER... */
 #endif
-		/* fall through - to _DRM_FRAME_BUFFER... */
 	case _DRM_FRAME_BUFFER:
 	case _DRM_REGISTERS:
 		offset = drm_core_get_reg_ofs(dev);
@@ -621,7 +621,7 @@ static int drm_mmap_locked(struct file *filp, struct vm_area_struct *vma)
 		    vma->vm_end - vma->vm_start, vma->vm_page_prot))
 			return -EAGAIN;
 		vma->vm_page_prot = drm_dma_prot(map->type, vma);
-		/* fall through - to _DRM_SHM */
+		fallthrough;	/* to _DRM_SHM */
 	case _DRM_SHM:
 		vma->vm_ops = &drm_vm_shm_ops;
 		vma->vm_private_data = (void *)map;