net: dcb: getnumtcs()/setnumtcs() should return an int

{g|s}etnumtcs() today returns a u8 that is only used by the DCB code
to verify no error occurred. Today the driver implementations return
negative error codes which end up being non-zero so the logic works
out but triggers some sparse warnings.

To fix the sparse warnings convert the return value to an int.

CC: Eilon Greenstein <eilong@broadcom.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>