Fix the following warnings:

ringbuf.rst:197: WARNING: Unknown target name: "bench_ringbuf.c"

There was no target defined for 'bench_ringbuf.c'. Also, the
syntax used was wrong, in the sense that it would not highlight
the entire path in the browser.

Signed-off-by: Daniel W. S. Almeida <dwlsalmeida@gmail.com>
---
 Documentation/bpf/ringbuf.rst | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Documentation/bpf/ringbuf.rst b/Documentation/bpf/ringbuf.rst
index 75f943f0009df..8e7c15a927740 100644
--- a/Documentation/bpf/ringbuf.rst
+++ b/Documentation/bpf/ringbuf.rst

@@ -200,10 +200,13 @@ a self-pacing notifications of new data being availability.
 being available after commit only if consumer has already caught up right up to
 the record being committed. If not, consumer still has to catch up and thus
 will see new data anyways without needing an extra poll notification.
-Benchmarks (see tools/testing/selftests/bpf/benchs/bench_ringbuf.c_) show that
+Benchmarks (see `tools/testing/selftests/bpf/benchs/bench_ringbufs.c`_) show that
 this allows to achieve a very high throughput without having to resort to