Bluetooth: Remove redundant check for req.cmd_q

The hci_req_run() function already checks for empty cmd_q and bails
out if necessary. Also, req.cmd_q should really be treated as private
data of the request and not accessed directly.

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