drm/i915: Remove dead code from skl_pipe_wm_get_hw_state()

There is nothing else to be executed after this if block.

Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210212182201.155043-2-jose.souza@intel.com