drm/i915/dmc: simplify intel_dmc_load_program() conditions

intel_dmc_load_program() is only ever called when
intel_dmc_has_payload() is true. Move the condition within
intel_dmc_load_program() to let it be called directly.

Also note that intel_dmc_has_payload() will always return false when
HAS_DMC() is false. Remove the redundant check.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c8ec46a44071f80b9c97617391b30e0c61ebc3e6.1647870374.git.jani.nikula@intel.com