drm/i915: Fix bit name in PP_STATUS register

According to the spec PP_SEQUENCE_STATE_ON_S1_1 is the correct name, so
just rename it.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190302011405.6405-1-lucas.demarchi@intel.com