Staging: olpc_dcon.c: obsolete use of strict_strtoul

As noted by the checkpatch script, strict_strtoul is obsolete. Unsigned
longs are used, so it seems good to take kstrtoul.

Signed-off-by: Valentin Rothberg <valentinrothberg@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>