drm: remove useless parameters from drm_pick_cmdline_mode function

drm_pick_cmdline_mode width and height parameters are useless.
Just remove them.

Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1483721084-20278-2-git-send-email-vincent.abriou@st.com