Change comment description for BluetoothGatt#registerApp

Current comment description says BluetoothGattCallback#onAppRegistered
will be triggered if the function returns true. However, this is no
longer true and the function simply moves on to client connection on
successful registration. Thus changing the description accordingly.

Bug: 343628924
Test: m com.android.btservices
Flag: EXEMPT, comment fix only
Change-Id: I769078c20d5d339822a4a9ac7661bfd0a1bb62e1