ixgbe: Use a signed type to hold error codes

ixgbe: Use a signed type to hold error codes

Orabug: 21669416

Because error codes are negative, it only makes sense to
consistently use signed types when handling them. Also remove
some explicit comparisons with 0 on these variables.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
(cherry picked from commit a1e869de72a7a6d9e1007d0b459e79e91f0cf5b5)
Signed-off-by: Brian Maly <brian.maly@oracle.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>