erofs: fix NULL dereference of dif->bdev_handle in fscache mode

mainline inclusion
from mainline-v6.7-rc3
commit 8bd90b6ae7856dd5000b75691d905b39b9ea5d6b
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KPBR
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.7-rc3&id=8bd90b6ae7856dd5000b75691d905b39b9ea5d6b



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Avoid NULL dereference of dif->bdev_handle, as dif->bdev_handle is NULL
in fscache mode.

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 RIP: 0010:erofs_map_dev+0xbd/0x1c0
 Call Trace:
  <TASK>
  erofs_fscache_data_read_slice+0xa7/0x340
  erofs_fscache_data_read+0x11/0x30
  erofs_fscache_readahead+0xd9/0x100
  read_pages+0x47/0x1f0
  page_cache_ra_order+0x1e5/0x270
  filemap_get_pages+0xf2/0x5f0
  filemap_read+0xb8/0x2e0
  vfs_read+0x18d/0x2b0
  ksys_read+0x53/0xd0
  do_syscall_64+0x42/0xf0
  entry_SYSCALL_64_after_hwframe+0x6e/0x76

Reported-by: Yiqun Leng <yqleng@linux.alibaba.com>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=7245


Fixes: 49845720080d ("erofs: Convert to use bdev_open_by_path()")
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20231114070704.23398-1-jefflexu@linux.alibaba.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>