ixgbe: fix ixgbe_fc_autoneg_fiber bug

A logic error in ixgbe_fc_autoneg_fiber() that treated a masked u32 as a
boolean would make it so we would never fall hit a error check case.  So
now I force the u32 to a boolean value with '!!'.

Signed-off-by: Don Skidmore <donald.c.skidmore@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>