ixgbe: fix to use correct timeout interval for memory read completion

Currently we were just always polling for a hard coded 80 ms and not
respecting the system-wide timeout interval.  Since up until now all
devices have been tested with this 80ms value we continue to use this
value as a hard minimum.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>