Bluetooth: Fix breakage in amp_write_rem_assoc_frag()

We should be passing the pointer itself instead of the address of the
pointer.

This was a copy and paste bug when we replaced the calls to
hci_send_cmd().  Originally, the arguments were "len, cp" but we
overwrote them with "sizeof(cp), &cp" by mistake.

Fixes: b3d39140 ('Bluetooth: Move amp assoc read/write completed callback to amp.c')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>