md/raid10: fix slab-out-of-bounds in md_bitmap_get_counter

hulk inclusion
category: bugfix
bugzilla: 188270, https://gitee.com/openeuler/kernel/issues/I6ECES


CVE: NA

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There is a bug if we write a large number to md/bitmap_set_bits.
md_bitmap_checkpage() returned -EINVAL if "page >= bitmap->pages", but the
return value was not checked immediately in md_bitmap_get_counter() in
order to set *blocks value. fix it by checking page before operate
bitmap.

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>