rio: Drop __DATE__ usage

The kernel already prints its build timestamp during boot, no need to
repeat it in random drivers and produce different object files each
time. As the buildDate field is part of the userspace API, I replaced it
with the date of the last code change.

Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Michal Marek <mmarek@suse.cz>