If the PCI connection is broken, reading the FW version string
will only get 0xff bytes, which shouldn't get printed.  This
checks the first byte and prints only the first 4 bytes
if non-ASCII.

Also, add a limit to the string length printed when a valid
string is found, just in case it is not properly terminated.
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>