transmission: add 'incomplete' and 'watch' dirs to ujail mounts

transmission: add 'incomplete' and 'watch' dirs to ujail mounts

To fix the errors:

Sun Apr 10 14:19:41 2022 daemon.err transmission-daemon[29831]: [2022-04-10 14:19:41.098] watchdir Failed to open directory "/mnt/sda1/openwrt/transmission/watch" (2): No such file or directory (watchdir.c:358)

and

Sun Apr 10 14:20:18 2022 daemon.err transmission-daemon[30175]: [2022-04-10 14:20:18.641] Couldn't create "/mnt/sda1/openwrt/transmission/incomplete": Permission denied (file-posix.c:243)

References:
- https://github.com/openwrt/packages/issues/17674

Signed-off-by: Alexander Egorenkov <egorenar-dev@posteo.net>