drm/i915: Simplify error handling in __intel_set_mode()

drm/i915: Simplify error handling in __intel_set_mode()

The remaining parts of the failure path could only be reached if the
allocation of crtc_state_copy would fail. In that case, there is nothing
to undo, so just get rid of the label for error handling and return an
error code immediately.

We also always allocate a pipe_config, even if the pipe is being
disabled, so the remaining part of what was the error/done case can be
simplified a little too.

v2: Ignore return value from drm_plane_helper_update(). (Ander)

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>