drm/amd/display: Fix exception from AUX acquire failure

[Why]
AUX arbitration occurs between SW and FW components.
When AUX acquire fails, it causes engine->ddc to be NULL,
which leads to an exception when we try to release the AUX
engine.

[How]
When AUX engine acquire fails, it should return from the
function without trying to continue the operation.
The upper level will determine if it wants to retry.
i.e. dce_aux_transfer_with_retries will be used and retry.
Signed-off-by: Anthony Koo <Anthony.Koo@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -374,7 +374,6 @@ static bool acquire(
 	struct dce_aux *engine,
 	struct ddc *ddc)
 {
-
 	enum gpio_result result;
 
 	if (!is_engine_available(engine))
@@ -455,7 +454,8 @@ int dce_aux_transfer(struct ddc_service *ddc,
 	memset(&aux_rep, 0, sizeof(aux_rep));
 
 	aux_engine = ddc->ctx->dc->res_pool->engines[ddc_pin->pin_data->en];
-	acquire(aux_engine, ddc_pin);
+	if (!acquire(aux_engine, ddc_pin))
+		return -1;
 
 	if (payload->i2c_over_aux)
 		aux_req.type = AUX_TRANSACTION_TYPE_I2C;