minigbm: Use the stride value returned by mapImage

mapImage can return a different stride value. This value must be
used for the mapped address.

BUG=b:38152101 b:79346377
TEST=graphics_Sanity autotest passed

Change-Id: Ie0eb716291366ae6a047d704f66d24ec41738713
Signed-off-by: Satyajit Sahu <satyajit.sahu@amd.com>
Reviewed-on: https://chromium-review.googlesource.com/1041369
Commit-Ready: Bernie Thompson <bhthompson@chromium.org>
Tested-by: Drew Davenport <ddavenport@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
diff --git a/drv.h b/drv.h
index 67d763e..9ca77d3 100644
--- a/drv.h
+++ b/drv.h
@@ -84,6 +84,7 @@
 	uint32_t handle;
 	uint32_t map_flags;
 	int32_t refcount;
+	uint32_t map_strides[DRV_MAX_PLANES];
 	void *priv;
 };