sfc: fix a timeout loop

We test for if "tries" is zero at the end but "tries--" is a post-op so
it will end with "tries" set to -1.  I have changed it to a pre-op
instead.

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