bta: Properly initialize bta::dm::disc::bta_dm_search_cb am: 100f3d68

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Bluetooth/+/2825175



Change-Id: Ie8e2cc41b09abfe69f12e6d3addd29a25155fadd
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>