Bluetooth: ISO: Rename bt_iso_cig_create_param

Renames the struct from bt_iso_cig_create_param to
bt_iso_cig_param as the same struct can, without
modification, be used to update the CIG as well
(function to support that will come in a later commit).

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>