block/vvfat: Plug memory leak in enable_write_target()

I figure the leak originated in bdrv_create2(), and was duplicated
into callers when commit 91a073a dropped that function.  Looks like
the other places have since been fixed.

Spotted by Coverity.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Benoit Canet <benoit@irqsave.net>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/vvfat.c

@@ -2929,6 +2929,7 @@ static int enable_write_target(BDRVVVFATState *s, Error **errp)
     set_option_parameter(options, BLOCK_OPT_BACKING_FILE, "fat:");
 
     ret = bdrv_create(bdrv_qcow, s->qcow_filename, options, errp);
+    free_option_parameters(options);
     if (ret < 0) {
         goto err;
     }