rules: add a missing comma in 70-uaccess.rules since it improves readability

rules: add a missing comma in 70-uaccess.rules since it improves readability

rule-syntax-check.py failed with the following error:

$ ./test/rule-syntax-check.py ./src/login/70-uaccess.rules
Invalid line ./src/login/70-uaccess.rules:31: SUBSYSTEM=="sound", TAG+="uaccess"   OPTIONS+="static_node=snd/timer", OPTIONS+="static_node=snd/seq"
  clause: TAG+="uaccess"   OPTIONS+="static_node=snd/timer"

The comma is actually optional but the script makes it mandatory which seems a
good thing since it improves readability.