drm/i915/display: fix phy name

Pass the correct variable as argument.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Clinton Taylor <Clinton.A.Taylor@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191217230529.25092-3-lucas.demarchi@intel.com