Bluetooth: Fix sparse warnings in RFCOMM

This patch fixes the following sparse warnings in rfcomm/core.c:

net/bluetooth/rfcomm/core.c:391:16: warning: dubious: x | !y
net/bluetooth/rfcomm/core.c:546:24: warning: dubious: x | !y

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