OpenFirmware: Make of_milliseconds() return error

The only user of of_milliseconds(), the boot loader's system_time(),
checks for an error that would never be signalled since the zero-initialized
number of milliseconds would always be returned.

Return OF_FAILED instead to allow explicit error handling in that case.

While this is a behavioral change, it is not yet a functional change,
for system_time()'s implementation translates OF_FAILED back to zero currently.

Resolves part of ticket #6061.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@37279 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/system/kernel/platform/openfirmware/openfirmware.cpp

@@ -559,7 +559,8 @@ of_milliseconds(void)
 		int			milliseconds;
 	} args = {"milliseconds", 0, 1, 0};
 
-	gCallOpenFirmware(&args);
+	if (gCallOpenFirmware(&args) == OF_FAILED)
+		return OF_FAILED;
 
 	return args.milliseconds;
 }