firewire: cdev: normalize variable names

Unify some names:
  - "e" for pointers to subtypes of struct event,
  - "event" for struct members and pointers to struct event,
  - "r" for pointers to subtypes of struct client_resource,
  - "resource" for struct members and pointers to struct client_resource,
  - other names for struct members and pointers to other types.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>