rtc: interface: Alarm race handling should not discard preceding error

Commit 795cda8338ea ("rtc: interface: Fix long-standing race when setting
alarm") should not discard any errors from the preceding validations.

Prior to that commit, if the alarm feature was disabled, or the
set_alarm failed, a meaningful error code would be returned to the
caller for further action.

After, more often than not, the __rtc_read_time will cause a success
return code instead, misleading the caller.

An example of this is when timer_enqueue is called for a rtc-abx080x
device. Since that driver does not clear the alarm feature bit, but
instead relies on the set_alarm operation to return invalid, the discard
of the return code causes very different behaviour; i.e.
hwclock: select() to /dev/rtc0 to wait for clock tick timed out

Fixes: 795cda8338ea ("rtc: interface: Fix long-standing race when setting alarm")
Signed-off-by: Anthony Pighin (Nokia) <[e-mail]>
Reviewed-by: Esben Haabendal <[e-mail]>
Tested-by: Nick Bowler <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/interface.c

···
 	 * are in, we can return -ETIME to signal that the timer has already
 	 * expired, which is true in both cases.
 	 */
-	if ((scheduled - now) <= 1) {
+	if (!err && (scheduled - now) <= 1) {
 		err = __rtc_read_time(rtc, &tm);
 		if (err)
 			return err;