change pdTrue(FreeRTOS) to osOS (CMSISOS) (#33017)

diff --git a/examples/platform/silabs/efr32/uart.cpp b/examples/platform/silabs/efr32/uart.cpp
index 2b29cca..9a626e1 100644
--- a/examples/platform/silabs/efr32/uart.cpp
+++ b/examples/platform/silabs/efr32/uart.cpp
@@ -442,7 +442,7 @@
     {
 
         osStatus_t eventReceived = osMessageQueueGet(sUartTxQueue, &workBuffer, nullptr, osWaitForever);
-        while (eventReceived == pdTRUE)
+        while (eventReceived == osOK)
         {
             uartSendBytes(workBuffer.data, workBuffer.length);
             eventReceived = osMessageQueueGet(sUartTxQueue, &workBuffer, nullptr, 0);