drm: use noop_llseek

The drm device drivers currently allow seeking on the
character device but never care about the actual
file position.

When we change the default llseek operation to be
no_llseek, calling llseek on a drm device would
return an error condition, which is an API change.

Explicitly setting noop_llseek lets us keep the
current API.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org

Documentation/DocBook/drm.tmpl

@@ -136,6 +136,7 @@
 #ifdef CONFIG_COMPAT
 		.compat_ioctl = i915_compat_ioctl,
 #endif
+		.llseek = noop_llseek,
 		},
 	.pci_driver = {
 		.name = DRIVER_NAME,