[PATCH 3/5] pi_stress: Improve error message for permission failures

When pi_stress fails to set real-time scheduling priority, it printed
a cryptic hex error code (0x1) that didn't explain what went wrong or
how to fix it.

Replace the error message with a clear explanation that indicates the
failure reason and suggests running with root privileges.

Before:
    main: boosting to max priority: 0x1

After:
    Failed to set real-time priority: Operation not permitted
    Please run with root privileges to set real-time priorities.

Assisted-by: Claude:claude-sonnet-4-5
Signed-off-by: John Kacur <[email protected]>
---
 src/pi_tests/pi_stress.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/pi_tests/pi_stress.c b/src/pi_tests/pi_stress.c
index c8c895a71e44..675953923c3a 100644
--- a/src/pi_tests/pi_stress.c
+++ b/src/pi_tests/pi_stress.c
@@ -134,8 +134,8 @@ int main(int argc, char **argv)
 	status = pthread_setschedparam(pthread_self(), admin_sa.sched_policy,
 				       &thread_param);
 	if (status) {
-		pi_error("%s: boosting to max priority: 0x%x\n", __func__,
-			 status);
+		pi_error("Failed to set real-time priority: %s\n", strerror(status));
+		pi_error("Please run with root privileges to set real-time priorities.\n");
 		return FAILURE;
 	}
 	/* block unwanted signals */
-- 
2.54.0