drm/i915/icl: Fix DSS_CTL register names

This patch fixes the naming of the registers:

s/PIPE_DSS_CTL/ICL_PIPE_DSS_CTL

And also fix the hex values to lower case, to match
rest of the definitions.

Manasi noticed this with the patch that was merged.

v2: fix "Fixes" tag.

Fixes: 8b1b558d ("drm/i915/icl: Add DSS_CTL Registers")
Suggested-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: Jani Nikula <jani.nikula@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: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101214216.8958-1-anusha.srivatsa@intel.com