meta-quanta: s6q: Fix syntax in phosphor-watchdog_%.bbappend

The phosphor-watchdog_%.bbappend has a syntax error of colon.

Tested:
built image successfully and solved the warning message.

Signed-off-by: Joseph Fu <joseph.fu@quantatw.com>
Change-Id: If8bd002e6f140c145c56b7bd0964ad415158d619