rtc: remove useless DRV_VERSION

rtc: remove useless DRV_VERSION

Many drivers are defining a DRV_VERSION. This is often only used for
MODULE_VERSION and sometimes to print an info message at probe time. This
is kind of pointless as they are all versionned with the kernel anyway.
Also the core will print a message when a new rtc is found.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>