drm/i915: Do not enable PSR in the next modeset after a error

When we detect a error and disable PSR, it is kept disabled until the
next modeset but as the sink already show signs that it do not
properly work with PSR lets disabled it for good to avoid any
additional flickering.

Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181121225441.18785-3-jose.souza@intel.com