[MIPS] Switch from to_tm to rtc_time_to_tm

This replaces the MIPS-specific to_tm function with the generic
rtc_time_to_tm function.  The big difference between the two functions is
that rtc_time_to_tm uses epoch 70 while to_tm uses 1970, so the result of
rtc_time_to_tm needs to be fixed up.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip22/ip22-time.c b/arch/mips/sgi-ip22/ip22-time.c
index 0387c38..c494180 100644
--- a/arch/mips/sgi-ip22/ip22-time.c
+++ b/arch/mips/sgi-ip22/ip22-time.c
@@ -29,7 +29,7 @@
 #include <asm/sgi/ip22.h>
 
 /*
- * note that mktime uses month from 1 to 12 while to_tm
+ * Note that mktime uses month from 1 to 12 while rtc_time_to_tm
  * uses 0 to 11.
  */
 unsigned long read_persistent_clock(void)
@@ -66,10 +66,10 @@
 	unsigned int save_control;
 	unsigned long flags;
 
-	to_tm(tim, &tm);
+	rtc_time_to_tm(tim, &tm);
 
 	tm.tm_mon += 1;		/* tm_mon starts at zero */
-	tm.tm_year -= 1940;
+	tm.tm_year -= 40;
 	if (tm.tm_year >= 100)
 		tm.tm_year -= 100;