bnx2x: Prevent probe as early as possible

It's possible that due to errors [either on PCI or on device itself]
registers reads would fail, returning all-Fs.

This adds a check as early as possible so that driver will not read junk
values and make incorrect probe decisions according to them; instead,
gracefully fail the probe.

Signed-off-by: Yuval Mintz <Yuval.Mintz@qlogic.com>
Signed-off-by: Ariel Elior <Ariel.Elior@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>