perf lock: Fix return code for functions in __cmd_contention

perf lock contention returns zero exit value even if the lock contention
BPF setup failed.

  # ./perf lock con -b true
  libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
  libbpf: failed to find '.BTF' ELF section in /lib/modules/6.13.0-rc3+/build/vmlinux
  libbpf: failed to find valid kernel BTF
  libbpf: kernel BTF is missing at '/sys/kernel/btf/vmlinux', was CONFIG_DEBUG_INFO_BTF enabled?
  libbpf: failed to find '.BTF' ELF section in /lib/modules/6.13.0-rc3+/build/vmlinux
  libbpf: failed to find valid kernel BTF
  libbpf: Error loading vmlinux BTF: -ESRCH
  libbpf: failed to load object 'lock_contention_bpf'
  libbpf: failed to load BPF skeleton 'lock_contention_bpf': -ESRCH
  Failed to load lock-contention BPF skeleton
  lock contention BPF setup failed
  # echo $?
   0

Fix this by saving the return code for lock_contention_prepare
so that command exits with proper return code. Similarly set the
return code properly for two other functions in builtin-lock, namely
setup_output_field() and select_key().

Signed-off-by: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20250110093730.93610-1-atrajeev@linux.vnet.ibm.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>

Author: athira-rajeev

tools/perf/builtin-lock.c

@@ -2049,7 +2049,8 @@ static int __cmd_contention(int argc, const char **argv)
 				goto out_delete;
 		}
 
-		if (lock_contention_prepare(&con) < 0) {
+		err = lock_contention_prepare(&con);
+		if (err < 0) {
 			pr_err("lock contention BPF setup failed\n");
 			goto out_delete;
 		}
@@ -2070,10 +2071,14 @@ static int __cmd_contention(int argc, const char **argv)
 		}
 	}
 
-	if (setup_output_field(true, output_fields))
+	err = setup_output_field(true, output_fields);
+	if (err) {
+		pr_err("Failed to setup output field\n");
 		goto out_delete;
+	}
 
-	if (select_key(true))
+	err = select_key(true);
+	if (err)
 		goto out_delete;
 
 	if (symbol_conf.field_sep) {