drm: nouveau: fix nouveau_debugfs_init prototype

The new debugfs initialization code fails to build when CONFIG_DEBUG_FS
is disabled:

In file included from /git/arm-soc/drivers/gpu/drm/nouveau/nouveau_drm.c:57:0:
drivers/gpu/drm/nouveau/nouveau_debugfs.h: In function 'nouveau_debugfs_init':
drivers/gpu/drm/nouveau/nouveau_debugfs.h:37:29: error: parameter name omitted
 nouveau_debugfs_init(struct nouveau_drm *)

This fixes the prototypes so we can build it again.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: b126a200 ("drm/nouveau/debugfs: we need a ctrl object for debugfs")
Signed-off-by: Dave Airlie <airlied@redhat.com>