capabilities:: annotate implicit fall through

capabilities:: annotate implicit fall through

There is a plan to build the kernel with -Wimplicit-fallthrough and
this place in the code produced a warning (W=1).

In this particular case change put the fall through comment on a single
line so as to match the regular expression expected by GCC.

This commit remove the following warning:

  kernel/capability.c:95:3: warning: this statement may fall through [-Wimplicit-fallthrough=]

Signed-off-by: Mathieu Malaterre <malat@debian.org>
Signed-off-by: James Morris <james.morris@microsoft.com>