ion: Add missing unlock on error path

A mutex_unlock was missing for the alloc_lock on an error
path. Add it.

Change-Id: If88b72fbc2fd18504347b784d5daa2bc9170c55f
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
diff --git a/drivers/gpu/ion/ion_cma_secure_heap.c b/drivers/gpu/ion/ion_cma_secure_heap.c
index d375c00..0aef596 100644
--- a/drivers/gpu/ion/ion_cma_secure_heap.c
+++ b/drivers/gpu/ion/ion_cma_secure_heap.c
@@ -446,6 +446,7 @@
 	if (ret) {
 		ret = ion_secure_cma_add_to_pool(sheap, len);
 		if (ret) {
+			mutex_unlock(&sheap->alloc_lock);
 			dev_err(sheap->dev, "Fail to allocate buffer\n");
 			goto err;
 		}