bnx2x: Warn about grc timeouts in register dump

There are several scenarios where taking a register dump from a device
might log benign GRC timeout attentions to system logs.
Most common of those is when taking the dump from a 2-port device.

Sadly, there's no easy way to mask the problematic attentions during the
flow - Changing this behvaior would require a firmware update.
For now, simply warn users to ignore the warnings.

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