time, drivers/rtc: Don't bother with rtc_resume() for the nonstop clocksource

If a system does not provide a persistent_clock(), the time
will be updated on resume by rtc_resume(). With the addition
of the non-stop clocksources for suspend timing, those systems
set the time on resume in timekeeping_resume(), but may not
provide a valid persistent_clock().

This results in the rtc_resume() logic thinking no one has set
the time and it then will over-write the suspend time again,
which is not necessary and only increases clock error.

So, fix this for rtc_resume().

This patch also improves the name of persistent_clock_exist to
make it more grammatical.

Change-Id: I3e666ddf354174ded759558f47a63a8013a84c1e
Signed-off-by: Xunlei Pang <pang.xunlei@linaro.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1427945681-29972-19-git-send-email-john.stultz@linaro.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>
[neeraju@codeaurora.org: Resolve merge conflicts]
Git-commit: 0fa88cb4b82b5cf7429bc1cef9db006ca035754e
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>