Bluetooth: btle: Clear info column before use it

This fix "btle" over "ubertooth" dissector, so messeges from both
will not be merged.

Change-Id: I587b81a405f37d16e8ab417d94edfc633bfc14fc
Reviewed-on: https://code.wireshark.org/review/3877
Petri-Dish: Michal Labedzki <michal.labedzki@tieto.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Evan Huus <eapache@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>