comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large

In the Linux kernel, the following vulnerability has been resolved: comedi: Fail COMEDI_INSNLIST ioctl if n_insns is too large The handling of the `COMEDI_INSNLIST` ioctl allocates a kernel buffer to hold the array of `struct comedi_insn`, getting the length from the `n_insns` member of the `struct comedi_insnlist` supplied by the user. The allocation will fail with a WARNING and a stack dump if it is too large. Avoid that by failing with an `-EINVAL` error if the supplied `n_insns` value is unreasonable. Define the limit on the `n_insns` value in the `MAX_INSNS` macro. Set this to the same value as `MAX_SAMPLES` (65536), which is the maximum allowed sum of the values of the member `n` in the array of `struct comedi_insn`, and sensible comedi instructions will have an `n` of at least 1.