erofs: avoid using multiple devices with different type

In the Linux kernel, the following vulnerability has been resolved:

erofs: avoid using multiple devices with different type

For multiple devices, both primary and extra devices should be the

same type. `erofs_init_device` has already guaranteed that if the

primary is a file-backed device, extra devices should also be

regular files.

However, if the primary is a block device while the extra device

is a file-backed device, `erofs_init_device` will get an ENOTBLK,

which is not treated as an error in `erofs_fc_get_tree`, and that

leads to an UAF:

erofs_fc_get_tree

get_tree_bdev_flags(erofs_fc_fill_super)

erofs_read_superblock

erofs_init_device // sbi->dif0 is not inited yet,

// return -ENOTBLK

deactivate_locked_super

free(sbi)

if (err is -ENOTBLK)

sbi->dif0.file = filp_open() // sbi UAF

So if -ENOTBLK is hitted in `erofs_init_device`, it means the

primary device must be a block device, and the extra device

is not a block device. The error can be converted to -EINVAL.