Bluetooth: Refactor read_ext_controller_info handler

There is no need to allocate heap for reply only to copy stack data to
it. This also fix rp memory leak and missing hdev unlock if kmalloc
failed.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>