Bluetooth: Fix errors and warnings in L2CAP reported by checkpatch.pl

This patch fixes the errors without changing the l2cap.o binary:

 text    data     bss     dec     hex filename
18059     568       0   18627    48c3 l2cap.o.after
18059     568       0   18627    48c3 l2cap.o.before

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>