Doc: networking/device_drivers/pensando: fix ionic.rst warnings

Fix documentation build warnings for Pensando ionic:

Documentation/networking/device_drivers/pensando/ionic.rst:39: WARNING: Unexpected indentation.
Documentation/networking/device_drivers/pensando/ionic.rst:43: WARNING: Unexpected indentation.

Fixes: df69ba43 ("ionic: Add basic framework for IONIC Network device driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>