[POWERPC] Fix timekeeping on PowerPC 601

Recent changes to the timekeeping code broke support for the PowerPC 601
processor which doesn't have the usual timebase facility but a slightly
different thing called (yuck) the RTC.

This fixes it, boot tested on an old 601 based PowerMac 7200.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>
diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
index d7f5ddf..c104c15 100644
--- a/include/asm-powerpc/time.h
+++ b/include/asm-powerpc/time.h
@@ -149,6 +149,11 @@
 }
 #endif /* !CONFIG_PPC64 */
 
+static inline u64 get_tb_or_rtc(void)
+{
+	return __USE_RTC() ? get_rtc() : get_tb();
+}
+
 static inline void set_tb(unsigned int upper, unsigned int lower)
 {
 	mtspr(SPRN_TBWL, 0);