bpf/benchs/bench_ringbufs: Remove unneeded semicolon

Eliminate the following coccicheck warning:
./tools/testing/selftests/bpf/benchs/bench_ringbufs.c:322:2-3: Unneeded
semicolon

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/1612684360-115910-1-git-send-email-yang.lee@linux.alibaba.com

tools/testing/selftests/bpf/benchs/bench_ringbufs.c

@@ -319,7 +319,7 @@ static void ringbuf_custom_process_ring(struct ringbuf_custom *r)
 			smp_store_release(r->consumer_pos, cons_pos);
 		else
 			break;
-	};
+	}
 }
 
 static void *ringbuf_custom_consumer(void *input)