[mesa] Add comment for overloaded parameter.

Change-Id: Ia131cc7e3f9509177ede8ed33c7f78f6b27f5929
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/991872
Reviewed-by: Craig Stout <cstout@google.com>
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/1005915
Commit-Queue: Josh Gargus <jjosh@google.com>
Reviewed-by: Alice Neels <neelsa@google.com>
Reviewed-by: Josh Gargus <jjosh@google.com>
diff --git a/src/vulkan/runtime/vk_magma_syncobj.c b/src/vulkan/runtime/vk_magma_syncobj.c
index ea720e0..943846c 100644
--- a/src/vulkan/runtime/vk_magma_syncobj.c
+++ b/src/vulkan/runtime/vk_magma_syncobj.c
@@ -51,6 +51,9 @@
    magma_status_t status;
    if (initial_value && initial_value != 1) {
       assert((initial_value >> 32) == 0);
+
+      // |initial_value| has been overloaded such that the Zircon handle
+      // is passed through it which in turn is passed to the import below.
       status = magma_connection_import_semaphore2(
          device->magma_connection->connection,
          (uint32_t)initial_value, /*flags=*/0, &sobj->semaphore, &sobj->id);