drm/nouveau/fifo: set gf100_fifo_nonstall_block_dump storage-class-specifier to static

gcc with W=1 reports
drivers/gpu/drm/nouveau/nvkm/engine/fifo/gf100.c:451:1: error:
  no previous prototype for ‘gf100_fifo_nonstall_block’ [-Werror=missing-prototypes]
  451 | gf100_fifo_nonstall_block(struct nvkm_event *event, int type, int index)
      | ^~~~~~~~~~~~~~~~~~~~~~~~~

gf100_fifo_nonstall_block is only used in gf100.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/20230303132731.1919329-1-trix@redhat.com