vrtc: change its year offset from 1960 to 1972

vrtc: change its year offset from 1960 to 1972

Real world year equals the value in vrtc YEAR register plus an offset.
We used 1960 as the offset to make leap year consistent, but for a
device's first use, its YEAR register is 0 and the system year will
be parsed as 1960 which is not a valid UNIX time and will cause many
applications to fail mysteriously. So use 1972 instead to fix this
issue.

Updated patch which adds a sanity check suggested by Mathias

Change-Id: I521271ac79b5657e9b9eb4a81fe6b2e5f5e94e0b
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>