rpmsg: glink: Unlock on error in qcom_glink_request_intent()

If qcom_glink_tx() fails, then we need to unlock before returning the
error code.

Fixes: 27b9c5b6

 ("rpmsg: glink: Request for intents when unavailable")
Acked-by: Sricharan R <sricharan@codeaurora.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>