staging: olpc_dcon: Remove _strtoul() function.

olpc_dcon driver use self invented _strtoul  function
which make similar check like strict_strtoul just extend
for space checking at last string place. Normally access
to sys file looks echo 1024 > /sys/... so space could be considered
as error character and we could simplify code using just strict_strtoul
function instead self invented.

Signed-off-by: Marek Belisko <marek.belisko@open-nandra.com>
Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>