drm/i915/dmc: remove redundant return in parse_csr_fw()

parse_csr_fw() is responsible to set up several fields in struct intel_csr,
including the payload. We don't need to assign it again.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190607091230.1489-9-lucas.demarchi@intel.com