drm/i915/bios: reduce indent in sanitize_ddc_pin and sanitize_aux_ch

Reduce indent with an early return. No functional changes.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
[Jani: fixed a couple of comment typos while applying.]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/17288137452f731a820e737582672f836660a26f.1615998927.git.jani.nikula@intel.com