kernel-doc: Fix example in Nested structs/unions

Add missing ';' as well as fixes the indent for the first struct.

Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>
Link: https://lore.kernel.org/r/20201207210027.1049346-1-ben.widawsky@intel.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>