Bluetooth: Remove mgmt_valid_hdev() helper function

The helper function mgmt_valid_hdev() is more obfuscating the code
then it makes it easier to read. So intead of this helper, use the
direct check for BR/EDR device type.

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