drm: Fix function names in kerneldoc

The drm_property_create_enum(), drm_property_create_bitmask() and
drm_property_create_range() contain the wrong name in the kerneldoc
comment. This is probably simply a copy/paste mistake.

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