drm/i915/dmc: s/intel_csr/intel_dmc

No functional change.

v2: Chchpatch fixes.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210518213444.11420-2-anusha.srivatsa@intel.com