fix(core): fix pm_suspend return value in case of stabilization TIMEOUT.

What changed, and why it matters

This is a one-line bug fix in the Trezor hardware wallet's power manager for STM32U5 chips. When the device timed out while waiting for its power state to stabilize, the function was accidentally returning the wrong value (false) instead of the proper error code (PM_TIMEOUT). This could cause callers to misinterpret a timeout as success, potentially mishandling power-state transitions. It is a correctness fix rather than an obvious exploit, but in embedded firmware such misreporting can contribute to reliability or security issues.

Security signals we found

Evidence from the diff

Changed components

diff --git a/core/embed/sys/power_manager/stm32u5/power_manager.c b/core/embed/sys/power_manager/stm32u5/power_manager.c
index 4e601867c..64a7a880d 100644
--- a/core/embed/sys/power_manager/stm32u5/power_manager.c
+++ b/core/embed/sys/power_manager/stm32u5/power_manager.c
@@ -293,7 +293,7 @@ pm_status_t pm_suspend(wakeup_flags_t* wakeup_reason) {
   pm_status_t status = pm_wait_to_stabilize(drv, PM_STABILIZATION_TIMEOUT_MS);
   if (status != PM_OK) {
     // timeout during state machine stabilization
-    return false;
+    return PM_TIMEOUT;
   }
 
   // TODO: Handle wake-up flags