docs/driver-model: fix typo

No need to be be, just be should be sufficient.
Signed-off-by: NLaurent Navet <laurent.navet@gmail.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/driver-model/device.txt

@@ -50,7 +50,7 @@ Attributes of devices can be exported by a device driver through sysfs.
 Please see Documentation/filesystems/sysfs.txt for more information
 on how sysfs works.
 
-As explained in Documentation/kobject.txt, device attributes must be be
+As explained in Documentation/kobject.txt, device attributes must be
 created before the KOBJ_ADD uevent is generated. The only way to realize
 that is by defining an attribute group.