firmware: qcom: uefisecapp: Fix deadlock in qcuefi_acquire()

If the __qcuefi pointer is not set, then in the original code, we would
hold onto the lock.  That means that if we tried to set it later, then
it would cause a deadlock.  Drop the lock on the error path.  That's
what all the callers are expecting.

Fixes: 759e7a2 ("firmware: Add support for Qualcomm UEFI Secure Application")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/19829bc4-1b6f-47f7-847a-e90c25749e40@stanley.mountain
Signed-off-by: Bjorn Andersson <andersson@kernel.org>

Author: Dan Carpenter

drivers/firmware/qcom/qcom_qseecom_uefisecapp.c

@@ -715,6 +715,10 @@ static int qcuefi_set_reference(struct qcuefi_client *qcuefi)
 static struct qcuefi_client *qcuefi_acquire(void)
 {
 	mutex_lock(&__qcuefi_lock);
+	if (!__qcuefi) {
+		mutex_unlock(&__qcuefi_lock);
+		return NULL;
+	}
 	return __qcuefi;
 }