Bluetooth: hci_conn: Remove redundant memset after kzalloc

Since kzalloc already zeroes the allocated memory, the subsequent
memset call is unnecessary. This patch removes the redundant memset to
clean up the code and enhance efficiency.

Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>