f2fs: fix null pointer panic in tracepoint in __replace_atomic_write_block

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

f2fs: fix null pointer panic in tracepoint in __replace_atomic_write_block

We got a kernel panic if old_addr is NULL.

https://bugzilla.kernel.org/show_bug.cgi?id=217266

BUG: kernel NULL pointer dereference, address: 0000000000000000

Call Trace:

<TASK>

f2fs_commit_atomic_write+0x619/0x990 [f2fs a1b985b80f5babd6f3ea778384908880812bfa43]

__f2fs_ioctl+0xd8e/0x4080 [f2fs a1b985b80f5babd6f3ea778384908880812bfa43]

? vfs_write+0x2ae/0x3f0

? vfs_write+0x2ae/0x3f0

__x64_sys_ioctl+0x91/0xd0

do_syscall_64+0x5c/0x90

entry_SYSCALL_64_after_hwframe+0x72/0xdc

RIP: 0033:0x7f69095fe53f