markers: break the redundant loop in kernel/marker.c

Impact: cleanup, no functionality changed

Because e->name is unique in list, we don't need to continue the iteration
after matched.

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>