greybus: es2: fix error return code in ap_probe()

Fix to return a negative error code from the es2_arpc_in_enable() error
handling case instead of 0, as done elsewhere in this function.

Fixes: 9d9d3777 ("greybus: es2: Add a new bulk in endpoint for APBridgeA RPC")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>