drm: Remove redundant code in the getencoder ioctl

drm: Remove redundant code in the getencoder ioctl

When enabling atomic state object for this ioctl in

commit abd69c55dd8f1f71b33b8c6165217f4329db8f25
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Nov 25 23:50:05 2014 +0100

    drm: Handle atomic state properly in kms getfoo ioctl

I've forgotten to remove this hunk in one of the later revisions.
drm_encoder_get_crtc already does this.

Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>