test/bpf: fix error message

This patch fixed wrong error variable in logging message.

Fixes: 83633ba23076 ("test/bpf: fix few small issues")
Cc: stable@dpdk.org

Signed-off-by: Min Hu (Connor) <humin29@huawei.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

app/test/test_bpf.c

@@ -3207,7 +3207,7 @@ run_test(const struct bpf_test *tst)
 			printf("%s@%d: check_result(%s) failed, "
 				"error: %d(%s);\n",
 				__func__, __LINE__, tst->name,
-				rv, strerror(ret));
+				rv, strerror(rv));
 		}
 	}