blockdev: Plug memory leak in drive_init()

bs_opts is leaked on all paths from its qdev_new() that don't got
through blockdev_init().  Add the missing QDECREF(), and zap bs_opts
after blockdev_init(), so the new QDECREF() does nothing when we go
through blockdev_init().

Leak introduced in commit f298d071.  Spotted by Coverity.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
(cherry picked from commit 3cb0e25c)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

blockdev.c

@@ -902,6 +902,7 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
 
     /* Actual block device init: Functionality shared with blockdev-add */
     dinfo = blockdev_init(filename, bs_opts, &local_err);
+    bs_opts = NULL;
     if (dinfo == NULL) {
         if (local_err) {
             qerror_report_err(local_err);
@@ -939,6 +940,7 @@ DriveInfo *drive_init(QemuOpts *all_opts, BlockInterfaceType block_default_type)
 
 fail:
     qemu_opts_del(legacy_opts);
+    QDECREF(bs_opts);
     return dinfo;
 }