Gralloc: Fall back to HW_CAMERA_WRITE if HW_VIDEO_ENCODER is not set.

In both video encoding and camera preview cases, HW_CAMERA_WRITE will
be set. This is a hack so that if HW_VIDEO_ENCODER is set, allocate
NV12 format; otherwise, allocate NV21 format.

Change-Id: I61dc96b125e026159f55048cb79783578832460a
diff --git a/libgralloc/gpu.cpp b/libgralloc/gpu.cpp
index 6759b55..c22ef5c 100644
--- a/libgralloc/gpu.cpp
+++ b/libgralloc/gpu.cpp
@@ -209,9 +209,9 @@
     // HAL_PIXEL_FORMAT_IMPLEMENTATION_DEFINED
     if(usage & GRALLOC_USAGE_HW_VIDEO_ENCODER)
         grallocFormat = HAL_PIXEL_FORMAT_YCbCr_420_SP; //NV12
-    if(usage & GRALLOC_USAGE_HW_CAMERA_READ)
+    else if(usage & GRALLOC_USAGE_HW_CAMERA_READ)
         grallocFormat = HAL_PIXEL_FORMAT_YCrCb_420_SP; //NV21
-    if(usage & GRALLOC_USAGE_HW_CAMERA_WRITE)
+    else if(usage & GRALLOC_USAGE_HW_CAMERA_WRITE)
         grallocFormat = HAL_PIXEL_FORMAT_YCrCb_420_SP; //NV21
 
     size = getBufferSizeAndDimensions(w, h, grallocFormat, alignedw, alignedh);