[build] Fix path to .git

Change-Id: Ic986b3e6ef9cd0f05b20b2b77cdb59007950184a
Reviewed-on: https://fuchsia-review.googlesource.com/c/third_party/mesa/+/642521
Reviewed-by: Craig Stout <cstout@google.com>
diff --git a/src/BUILD.gn b/src/BUILD.gn
index 6454c0d..000bbc6 100644
--- a/src/BUILD.gn
+++ b/src/BUILD.gn
@@ -138,7 +138,7 @@
   ]
 
   # Ensure that this action reruns when git HEAD moves
-  inputs = [ ".git/HEAD" ]
+  inputs = [ "../.git/HEAD" ]
 
   public_configs = [ ":sha1_config" ]
 }