drm/i915: Get rid of silly void* from MST code

Not sure why this thing is trying to avoid declaring the proper
type for these pointers. But since these are used only once let's
just get rid of the local variable entirely.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200310202752.28454-1-ville.syrjala@linux.intel.com


Reviewed-by: José Roberto de Souza <jose.souza@intel.com>