tslib: fix use of open()

Fixes error: "open with O_CREAT in second argument needs 3 arguments".

Original patch: svn://svn.berlios.de/tslib/trunk/tslib

 r72.

[Peter: pull original patch for proper attribution]
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>