selftest/bpf: Fix spelling mistake "SIGALARM" -> "SIGALRM"

There is a spelling mistake in an error message, fix it.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200514121529.259668-1-colin.king@canonical.com

tools/testing/selftests/bpf/bench.c

@@ -242,7 +242,7 @@ static void setup_timer()
 	last_time_ns = get_time_ns();
 	err = sigaction(SIGALRM, &sigalarm_action, NULL);
 	if (err < 0) {
-		fprintf(stderr, "failed to install SIGALARM handler: %d\n", -errno);
+		fprintf(stderr, "failed to install SIGALRM handler: %d\n", -errno);
 		exit(1);
 	}
 	timer_settings.it_interval.tv_sec = 1;