Fix byte-per-pixel for floating point color buffer

Change-Id: I0c881831bd64eadca07123d7f3fd93d87e5c0f5a
diff --git a/system/gralloc/gralloc.cpp b/system/gralloc/gralloc.cpp
index 2b9dcc5..b687c74 100644
--- a/system/gralloc/gralloc.cpp
+++ b/system/gralloc/gralloc.cpp
@@ -480,7 +480,7 @@
             break;
 #if PLATFORM_SDK_VERSION >= 26
         case HAL_PIXEL_FORMAT_RGBA_FP16:
-            bpp = 16;
+            bpp = 8;
             glFormat = GL_RGBA16F;
             glType = GL_HALF_FLOAT;
             break;