rtc: goldfish: Enable interrupt in set_alarm() when necessary

[ Upstream commit 22f8d5a1

 ]

When use goldfish rtc, the "hwclock" command fails with "select() to
/dev/rtc to wait for clock tick timed out". This is because "hwclock"
need the set_alarm() hook to enable interrupt when alrm->enabled is
true. This operation is missing in goldfish rtc (but other rtc drivers,
such as cmos rtc, enable interrupt here), so add it.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/1592654683-31314-1-git-send-email-chenhc@lemote.com
Signed-off-by: Sasha Levin <sashal@kernel.org>