module/event: Add missing keyring dep to event_bdev

Looks like for the event_bdev the subdirs_rule was never called for
the module/event/subsystems/keyring since its DEPDIRS was missing it.

This was noticed while building SPDK with a single make job where
all the deps are compiled one by one. See:

https://github.com/spdk/spdk/issues/3434



Fixes: #3434

Change-Id: Iedf23efe2cb45e7fe6d5e84341b48ad4f922f6b0
Signed-off-by: Michal Berger <michal.berger@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/24252


Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Community-CI: Mellanox Build Bot
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>