cxgb4: Signedness bug in init_one()

The "chip" variable is an enum, and it's treated as unsigned int by GCC
in this context so the error handling isn't triggered.

Fixes: e8d45292 ("cxgb4: clean up init_one")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>