OpenBSD: fix FTBS on misspelled and missing variables
../xf86drm.c:4622:9: error: use of undeclared identifier 'written'; did you mean 'write'? if (written + 1 > max_node_length) ^~~~~~~ write
../xf86drm.c:4624:21: error: use of undeclared identifier 'sbuf'; did you mean 'sbrk'? if (stat(node, &sbuf)) ^~~~
Signed-off-by: Enrico Weigelt, metux IT consult info@metux.net