net/cxgb4: Check the return from t4_query_params properly

Positive return values are also failures that don't set val,
although this probably can't happen. Fixes gcc 10 warning:

drivers/net/ethernet/chelsio/cxgb4/t4_hw.c: In function ‘t4_phy_fw_ver’:
drivers/net/ethernet/chelsio/cxgb4/t4_hw.c:3747:14: warning: ‘val’ may be used uninitialized in this function [-Wmaybe-uninitialized]
 3747 |  *phy_fw_ver = val;

Fixes: 01b69614 ("cxgb4: Add PHY firmware support for T420-BT cards")
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>