gpu: ion: minor refactor in ion_mmap

mutex_unlock is being called in the if and the else branch. Just move
it out of the if/else. This will help reduce upcoming merge conflicts
with upstream Ion changes.

Change-Id: Ib426e73f1cb9ed79f37b9c1e0a8885066ae5b4f4
Signed-off-by: Mitchel Humpherys <mitchelh@codeaurora.org>
diff --git a/drivers/gpu/ion/ion.c b/drivers/gpu/ion/ion.c
index 9ab2343..9128177 100644
--- a/drivers/gpu/ion/ion.c
+++ b/drivers/gpu/ion/ion.c
@@ -1248,14 +1248,12 @@
 	mutex_lock(&buffer->lock);
 	/* now map it to userspace */
 	ret = buffer->heap->ops->map_user(buffer->heap, buffer, vma);
+	mutex_unlock(&buffer->lock);
 
 	if (ret) {
-		mutex_unlock(&buffer->lock);
 		pr_err("%s: failure mapping buffer to userspace\n",
 		       __func__);
 	} else {
-		mutex_unlock(&buffer->lock);
-
 		vma->vm_ops = &ion_vm_ops;
 		/*
 		 * move the buffer into the vm_private_data so we can access it