drm/vgem: Simplify dumb_map

The offset manager already checks for existing offsets internally,
while holding suitable locks. We can drop this check.

v2: Fix title (Emil).
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459330852-27668-11-git-send-email-daniel.vetter@ffwll.ch

drivers/gpu/drm/vgem/vgem_drv.c

@@ -208,11 +208,9 @@ int vgem_gem_dumb_map(struct drm_file *file, struct drm_device *dev,
 		goto unlock;
 	}
 
-	if (!drm_vma_node_has_offset(&obj->vma_node)) {
 	ret = drm_gem_create_mmap_offset(obj);
 	if (ret)
 		goto unref;
-	}
 
 	BUG_ON(!obj->filp);