bnxt: fix unsigned comparsion with 0

Fixes warning because location is u32 and can never be netative
warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Acked-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>