mount: Fix parsing /etc/fstab on *BSD.

This completion is still just a stub on *BSD, but now at least it does not
look like a complete mistake.

completions/mount

@@ -53,7 +53,8 @@ _mount()
         # probably Cygwin
         COMPREPLY=( $( compgen -W "$( mount | awk '! /^[ \t]*#/ {if ($3 ~ /\//) print $3}' )" -- "$cur" ) )
     else
-        COMPREPLY=( $( compgen -W "$( awk '! /^[ \t]*#/ {if ($3 ~ /\//) print $3}' /etc/fstab )" -- "$cur" ) )
+        # probably BSD
+        COMPREPLY=( $( compgen -W "$( awk '! /^[ \t]*#/ {if ($2 ~ /\//) print $2}' /etc/fstab )" -- "$cur" ) )
     fi
 } &&
 complete -F _mount -o default -o dirnames mount