mm/sparse: add the missing sparse_buffer_fini() in error branch

sparse_buffer_init() and sparse_buffer_fini() should appear in pair, or a
WARN issue would be through the next time sparse_buffer_init() runs.

Add the missing sparse_buffer_fini() in error branch.

Link: https://lkml.kernel.org/r/20210325113155.118574-1-wangwensheng4@huawei.com
Fixes: 85c77f79

 ("mm/sparse: add new sparse_init_nid() and sparse_init()")
Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>