Fix: ic_fixed_rate is the index to rate of rs_rates[] from ic_sup_rates

I was setting ic_fixed_rate with rate value that user passed over ioctl
but it is wrong, ic_fixed_rate is not used to store current rate, but
instead it is used to store the index for whished rate of rs_rates.

Signed-off-by: Alan Carvalho de Assis <acassis@gmail.com>