drm/i915/dsc: Fix PPS register definition macros for 2nd VDSC engine

This patch fixes the PPS4 and PPS5 register definition macros that were
resulting into an incorect MMIO address.

Fixes: 2efbb2f0

 ("i915/dp/dsc: Add DSC PPS register definitions")
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180824014807.14681-1-manasi.d.navare@intel.com