asm-generic: make get_rtc_time overridable

Evidently, set_rtc_time is supposed to be overridable
by architectures that define their own version, but
unfortunately, get_rtc_ss would in that case still
use the generic version.

This makes get_rtc_ss call the real set_rtc_time
to let architectures define their own version.
The change should fix the "Extended RTC operation"
on Alpha, which uses the incorrect get_rtc_ss
call. It also allows PowerPC to use the asm-generic/rtc.h
file in the future.

Cc: Richard Henderson <[e-mail]>
Cc: [e-mail]
Cc: Tom Rini <[e-mail]>
Cc: [e-mail]
Cc: Alessandro Zummo <[e-mail]>
Cc: Paul Gortmaker <[e-mail]>
Signed-off-by: Arnd Bergmann <[e-mail]>

include/asm-generic/rtc.h

···
 {
 	struct rtc_time h;
 
-	__get_rtc_time(&h);
+	get_rtc_time(&h);
 	return h.tm_sec;
 }