bash-completion: Exclude /dev/fd from fsck find

bash-completion: Exclude /dev/fd from fsck find

When the bash-completion for fsck runs `find -L /dev/ -type b` it
descends into /dev/fd after opening '.' as file descriptor 3.  This
causes find to search through /dev/fd/3/ which includes everything below
the current directory, which can take a very long time.

To avoid this, prune /dev/fd in the find expression.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>