intel: Only check file type bits not mode when searching for rendernodes

Before checking st_rdev, we first need to validate that the file is a
device node, but we only want to check the file type bits and not
compare the permissions.

Reported-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>