drm/nouveau: fix kernel-doc comments

drm/nouveau: fix kernel-doc comments

Fix some malformed kernel-doc comments that were added in a recent commit.

Also, kernel-doc does not support global variables, so change those
kernel-doc comments into regular comments.

Fixes: 214c9539cf2f ("drm/nouveau: expose GSP-RM logging buffers via debugfs")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412310834.jtCJj4oz-lkp@intel.com/
Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Ben Skeggs <bskeggs@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250108234329.842256-1-ttabi@nvidia.com