Include what we use.

Test: mma
Bug: None
Change-Id: I3597c9173493d34b3e45e498f6a4a80f6bea5315
Exempt-From-Owner-Approval: trivial cleanup
diff --git a/vulkan/nulldrv/null_driver.cpp b/vulkan/nulldrv/null_driver.cpp
index b4ca42c..e2d5c83 100644
--- a/vulkan/nulldrv/null_driver.cpp
+++ b/vulkan/nulldrv/null_driver.cpp
@@ -16,6 +16,7 @@
 
 #include <hardware/hwvulkan.h>
 
+#include <errno.h>
 #include <inttypes.h>
 #include <stdlib.h>
 #include <string.h>