HID: hidraw: improve error handling in hidraw_init()

HID: hidraw: improve error handling in hidraw_init()

commit bcb4a75bde3821cecb17a71d287abfd6ef9bd68d upstream.

Several improvements in error handling:
- do not report success if alloc_chrdev_region() failed
- check for error code of cdev_add()
- use unregister_chrdev_region() instead of unregister_chrdev()
  if class_create() failed

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>