ubi: block: fix memleak in ubiblock_create()

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8P68G



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If idr_alloc() fails, dev->gd will be put after goto out_cleanup_disk in
ubiblock_create(), but dev->gd has not been assigned yet at this time, and
gd will not be put anymore. Fix it by putting gd directly.

Signed-off-by: Li Nan <linan122@huawei.com>