powerpc: Make set_rtc_time() return error code from lower-level function

Previously it ignored the return value from ppc_md.set_rtc_time,
but in fact the functions that that can point to do return a
useful error code, so return it from set_rtc_time().
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/rtc.h

@@ -52,10 +52,8 @@ static inline unsigned int get_rtc_time(struct rtc_time *time)
 /* Set the current date and time in the real time clock. */
 static inline int set_rtc_time(struct rtc_time *time)
 {
-	if (ppc_md.get_rtc_time) {
-		ppc_md.set_rtc_time(time);
-		return 0;
-	}
+	if (ppc_md.set_rtc_time)
+		return ppc_md.set_rtc_time(time);
 	return -EINVAL;
 }