efibootmgr: add missing break for 'u' case
Reviewed by: imp, zlei
Reported by: Coverity
CID: 1505695
Fixes: 9a7915299484 ("efibootmgr: Add --efidev (-u) to dis...")
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D38747
(cherry picked from commit 17a5a290032ef75ed4aa8a2aa68b3a7e08935c1c)