RG_IRQ_STATUS
rc = at86rf230_read_subreg(lp, RG_IRQ_STATUS, 0xff, 0, &status);
case RG_IRQ_STATUS:
case RG_IRQ_STATUS:
case RG_IRQ_STATUS:
ctx->buf[0] = (RG_IRQ_STATUS & CMD_REG_MASK) | CMD_REG;