drm/gem: Fix a few kerneldoc typos

While at it, adjust the drm_gem_handle_create() function declaration to
be more consistent with other functions in the file.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>

diff --cc drivers/gpu/drm/drm_gem.c
Simple merge