sdm: Fix memory leak in connector modes

HWDevice calls GetConnectorInfo twice without freeing the memory
allocated by libsdedrm in the first call. Move to using vectors.

Change-Id: Ie2e1372f441d21dfc397f0891fd59b007016fefe
CRs-fixed: 1114808
diff --git a/libdrmutils/drm_interface.h b/libdrmutils/drm_interface.h
index 35285ee..176c970 100644
--- a/libdrmutils/drm_interface.h
+++ b/libdrmutils/drm_interface.h
@@ -399,8 +399,7 @@
   uint32_t mmWidth;
   uint32_t mmHeight;
   uint32_t type;
-  uint32_t num_modes;
-  drmModeModeInfo *modes;
+  std::vector<drmModeModeInfo> modes;
   DRMTopology topology;
   std::string panel_name;
   DRMPanelMode panel_mode;