net:enetc: bug fix for qos sfi operate space after freed

'Dan Carpenter' reported:
This code frees "sfi" and then dereferences it on the next line:
>                 kfree(sfi);
>                 clear_bit(sfi->index, epsfp.psfp_sfi_bitmap);

This "sfi->index" should be "index".

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Po Liu <Po.Liu@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>