f2fs: fix null-ptr-deref in f2fs_submit_page_bio()

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

f2fs: fix null-ptr-deref in f2fs_submit_page_bio()

There's issue as follows when concurrently installing the f2fs.ko

module and mounting the f2fs file system:

KASAN: null-ptr-deref in range [0x0000000000000020-0x0000000000000027]

RIP: 0010:__bio_alloc+0x2fb/0x6c0 [f2fs]

Call Trace:

<TASK>

f2fs_submit_page_bio+0x126/0x8b0 [f2fs]

__get_meta_page+0x1d4/0x920 [f2fs]

get_checkpoint_version.constprop.0+0x2b/0x3c0 [f2fs]

validate_checkpoint+0xac/0x290 [f2fs]

f2fs_get_valid_checkpoint+0x207/0x950 [f2fs]

f2fs_fill_super+0x1007/0x39b0 [f2fs]

mount_bdev+0x183/0x250

legacy_get_tree+0xf4/0x1e0

vfs_get_tree+0x88/0x340

do_new_mount+0x283/0x5e0

path_mount+0x2b2/0x15b0

__x64_sys_mount+0x1fe/0x270

do_syscall_64+0x5f/0x170

entry_SYSCALL_64_after_hwframe+0x76/0x7e

Above issue happens as the biset of the f2fs file system is not

initialized before register "f2fs_fs_type".

To address above issue just register "f2fs_fs_type" at the last in

init_f2fs_fs(). Ensure that all f2fs file system resources are

initialized.