drm_hwcomposer: Store the HAL_PIXEL_FORMAT_* in the hwc_drm_bo

The new GraphicBufferMapper ImportBuffer takes a format
as an argument, but I believe it wants the HAL_PIXEL_FORMAT_*
and not the DRM_FORMAT value.

So stash the HAL_PIXEL_FORMAT_* into the hwc_drm_bo so we
can pass it along when needed.

Change-Id: Id5b8e0d8c624e26c2c6307f85489665c88a9e75d
Signed-off-by: John Stultz <john.stultz@linaro.org>
diff --git a/platformhisi.cpp b/platformhisi.cpp
index 99d222b..1723cb8 100644
--- a/platformhisi.cpp
+++ b/platformhisi.cpp
@@ -96,6 +96,7 @@
 
   bo->width = hnd->width;
   bo->height = hnd->height;
+  bo->hal_format = hnd->req_format;
   bo->format = fmt;
   bo->usage = hnd->usage;