BTM_BleClearBgConnDev -> BTM_WhiteListClear

BTM_WhiteList* functions are called only from gatt_utils.cc.
BTM_BleClearBgConnDev is currently an exception - instead of being
called from there, it does call gatt_reset_bgdev_list. This patch fixes
that.

Test: compilation, no functional change
Bug: 112827989
Change-Id: I4cd5bfee44c46d2ef37912496cd6cf5298ab1dfc