Silence test syfs option failure

If setting a sysfs option failes the bash write error is output.  It
contains the script line number which can fail over time, leading to
mismatched golden output failures if we used the output as an expected
indication of failure.  Callers should test its rc and output
accordingly if they want the failure logged and compared.

Signed-off-by: Zach Brown <zab@versity.com>

tests/funcs/fs.sh

@@ -400,7 +400,7 @@ t_set_sysfs_mount_option() {
 	local val="$3"
 	local opt="$(t_sysfs_path $nr)/mount_options/$name"
 
-	echo "$val" > "$opt"
+	echo "$val" > "$opt" 2>/dev/null
 }
 
 t_set_all_sysfs_mount_options() {