rtc: hctosys: do not treat lack of RTC device as error

When using device trees on the ARM platform, it is not certain at compile
time whether or not the system will have a RTC.

If one enables CONFIG_HCTOSYS just in case the system booted has a RTC,
and it turns out not to be, this will result in a big fat "unable to open
rtc device" error being printed to console, even when "quiet" is set in
the kernel cmdline.

Fix this by outputting the message with loglevel info instead.

Signed-off-by: Floris Bos <bos@je-eigen-domein.nl>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>