ixgbe: Remove unnecessary #ifdef CONFIG_DEBUG_FS tests

Add some empty static inlines instead to make
the code more readable.

Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>