bta: Fix using stored db to save reconnection time

Db is loaded in bta_gattc_conn which checks for RobustCaching
support using that loaded db. Then bta_gattc_start_discover is
called which also does the same check but with p_clcb->p_srcb->gatt_database
which is empty because it was only set if there was no support for
caching.

Bug: 274408908
Test: manual: listen to music via earbuds, put one in the case, take it
out and expect immediate reconnection.
Tag: #feature

Change-Id: I145518c7c867c1463065c4b3a912606fe4d3d0c4