ixgbevf: Make the ethtool register test use accessors

Make the ethtool register test use the normal register accessor
functions. Also eliminate macros used for calling register test
functions to make error exits clearer.

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>