drm/i915/dsc: Add missing _MMIO() from PPS registers

This patch fixes the commit -
<2efbb2f0> ("i915/dp/dsc: Add DSC PPS register definitions"),
which did not have _MMIO() for DSCA and DSCC.

v2: Fix typos. (manasi)

v3: Change the commit message (Rodrigo)

Cc: Rodrigi Vivi <rodrigo.vivi@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1532122962-9068-1-git-send-email-anusha.srivatsa@intel.com