graphics.h: clarify docs about stride for YV12
This change makes it clearer how to derive the stride of the Cr and Cb plane
from the stride of the Y plane for the YV12 pixel format.
Change-Id: I54a9a20f35224bd583e25c615014cc8d830a1dd0
diff --git a/include/system/graphics.h b/include/system/graphics.h
index e206e3e..24e2bfb 100644
--- a/include/system/graphics.h
+++ b/include/system/graphics.h
@@ -78,7 +78,8 @@
* - a vertical stride equal to the height
*
* y_size = stride * height
- * c_size = ALIGN(stride/2, 16) * height/2
+ * c_stride = ALIGN(stride/2, 16)
+ * c_size = c_stride * height/2
* size = y_size + c_size * 2
* cr_offset = y_size
* cb_offset = y_size + c_size