Bluetooth: fixing UBSAN warnings related to Codec Configuration

During local testing with UBSAN enabled, warning was reported:
bluetooth/host/iso.c:237:2: runtime error: null pointer passed
as argument 2, which is declared to never be null

It turned out that when datapath doesn't contain
codec information, cc_len is 0 and cc is NULL

In order to avoid UB,
now we call memcpy only when cp->codec_config_len > 0

Signed-off-by: Ivan Iushkov <ivan.iushkov@nordicsemi.no>