drm/nouveau/fifo: set nvkm_engn_cgrp_get storage-class-specifier to static

smatch reports
drivers/gpu/drm/nouveau/nvkm/engine/fifo/runl.c:33:18:
  warning: symbol 'nvkm_engn_cgrp_get' was not declared. Should it be static?

nvkm_engn_cgrp_get is only used in runl.c, so it should be static
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230228221533.3240520-1-trix@redhat.com

drivers/gpu/drm/nouveau/nvkm/engine/fifo/runl.c

@@ -30,7 +30,7 @@
 #include <subdev/timer.h>
 #include <subdev/top.h>
 
-struct nvkm_cgrp *
+static struct nvkm_cgrp *
 nvkm_engn_cgrp_get(struct nvkm_engn *engn, unsigned long *pirqflags)
 {
 	struct nvkm_cgrp *cgrp = NULL;