syszkaller fuzzer triggered a divide by zero, when set calibration
through ioctl().

To fix it, test 'bitrate' if it is negative or 0, just return -EINVAL.
Reported-by: NAndrey Konovalov <andreyknvl@google.com>
Signed-off-by: NFiro Yang <firogm@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>