rtos: fix print format specifiers

Exposed by arm-none-eabi build.

Change-Id: I657c642249aa83403f93132d1e28713aee692c30
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2724
Tested-by: jenkins

src/rtos/rtos.c

@@ -473,7 +473,7 @@ int rtos_generic_stack_read(struct target *target,
 		LOG_ERROR("Error reading stack frame from thread");
 		return retval;
 	}
-	LOG_DEBUG("RTOS: Read stack frame at 0x%x\r\n", address);
+	LOG_DEBUG("RTOS: Read stack frame at 0x%" PRIx32, address);
 
 #if 0
 		LOG_OUTPUT("Stack Data :");