dma-fence: Silence sparse warning in dma_fence_describe

dma-fence: Silence sparse warning in dma_fence_describe

Sparse complains about assigning a string to a __rcu annotated local
variable:

drivers/dma-buf/dma-fence.c:1040:38: warning: incorrect type in initializer (different address spaces)
drivers/dma-buf/dma-fence.c:1040:38:    expected char const [noderef] __rcu *timeline
drivers/dma-buf/dma-fence.c:1040:38:    got char *
drivers/dma-buf/dma-fence.c:1041:36: warning: incorrect type in initializer (different address spaces)
drivers/dma-buf/dma-fence.c:1041:36:    expected char const [noderef] __rcu *driver
drivers/dma-buf/dma-fence.c:1041:36:    got char *

It is harmless but lets silence it.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Fixes: ac364014fd81 ("dma-buf: cleanup dma_fence_describe v3")
Cc: Christian König <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20260415083207.40513-1-tvrtko.ursulin@igalia.com