Allow type conversion from YUVPlane to int

To get around the compiler error:

YUVConverter.cpp:243:57: error: format specifies type 'int' but the argument has type 'YUVPlane' [-Werror,-Wformat]

Bug: b/312565119

Change-Id: I7b833e7fff8d5730fe778ac51cc6787d0a152de0
diff --git a/host/gl/YUVConverter.h b/host/gl/YUVConverter.h
index 1a05f28..4276f9d 100644
--- a/host/gl/YUVConverter.h
+++ b/host/gl/YUVConverter.h
@@ -28,7 +28,7 @@
 namespace gfxstream {
 namespace gl {
 
-enum class YUVPlane {
+enum class YUVPlane : int {
     Y = 0,
     U = 1,
     V = 2,