drm/doc: Fix up some kms function names

A couple of the kms functions didn't have the correct/newest names.
This prevented them to be identified as refs in the html doc.

Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Tested-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170222084741.8485-1-architt@codeaurora.org