contrib/bash_completion.d: squelch FreeBSD seq when first < last

With seq x -1 z and x is less than z FreeBSD seq will print the error:

	$ seq 1 -1 2
	seq: needs positive increment

Hide this error.  Alternatively $COMP_CWORD could be checked for < 2.

Signed-off-by: Derek Schrock <dereks@lifeofadishwasher.com>

contrib/bash_completion.d/zfs.in

@@ -155,7 +155,7 @@ __zfs_list_volumes()
 __zfs_argument_chosen()
 {
     local word property
-    for word in $(seq $((COMP_CWORD-1)) -1 2)
+    for word in $(seq $((COMP_CWORD-1)) -1 2 2>/dev/null)
     do
         local prev="${COMP_WORDS[$word]}"
         if [[ ${COMP_WORDS[$word-1]} != -[tos] ]]