bluetooth: audio: delegator: Use BT_ATT_ERR_WRITE_REQ_REJECTED

If the total length of the opcode and parameter values of Broadcast
Receive State characteristic operation is incorrect, the server shall
respond with an ATT Error Response and the Error Code set to Write
Request Rejected (0xfc), instead of 0x0d
(BT_ATT_ERR_INVALID_ATTRIBUTE_LEN).

Signed-off-by: Magdalena Kasenberg <magdalena.kasenberg@codecoup.pl>