Bluetooth: Remove pointless check of hci_send_frame parameter

The hdev parameter of hci_send_frame must be always valid. If the hdev
is not valid, it would not even make it to this stage. The callers
will have already accessed hdev at that point many times.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>