drm/amd/display: Fix dmub_psr_destroy()

This is freeing the wrong variable so it will crash.  It should be
freeing "*dmub" instead of "dmub".

Fixes: 4c1a1335 ("drm/amd/display: Driverside changes to support PSR in DMCUB")
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dmub_psr.c

@@ -235,6 +235,6 @@ struct dmub_psr *dmub_psr_create(struct dc_context *ctx)
  */
 void dmub_psr_destroy(struct dmub_psr **dmub)
 {
-	kfree(dmub);
+	kfree(*dmub);
 	*dmub = NULL;
 }