drm/i915/dp: avoid shadowing variables

Everything seems to be all right, but shadowing is to be avoided.

Cc: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190820134019.13229-2-jani.nikula@intel.com