dma-buf: fix incorrect dma-fence documentation v2

dma-buf: fix incorrect dma-fence documentation v2

There isn't much worse than documentation giving an incorrect advise.
Grabbing a spinlock while interrupts are disabled usually means that you
must also disable interrupts for all other uses of this spinlock.

Otherwise really hard to debug issues can occur. So fix that invalid
documentation.

v2: use Dmitry's suggestion on the documentation

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch> (v1)
Link: https://patchwork.freedesktop.org/patch/msgid/20250211163109.12200-2-christian.koenig@amd.com