sksl: Use va_end() after va_copy()

We invoke va_end() as required when we're done with our va_copy().

Change-Id: Ibc55279c3bc01a63da2ef5f1942d46367eac8a67
Reviewed-on: https://skia-review.googlesource.com/c/191322
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
diff --git a/src/sksl/SkSLHCodeGenerator.cpp b/src/sksl/SkSLHCodeGenerator.cpp
index 8c6b8f4..cb8712e 100644
--- a/src/sksl/SkSLHCodeGenerator.cpp
+++ b/src/sksl/SkSLHCodeGenerator.cpp
@@ -110,6 +110,7 @@
         vsprintf(heap.get(), s, copy);
         fOut->write(heap.get(), length);
     }
+    va_end(copy);
 }
 
 void HCodeGenerator::writef(const char* s, ...) {