dm-integrity: Avoid divide by zero in table status in Inline mode

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

dm-integrity: Avoid divide by zero in table status in Inline mode

In Inline mode, the journal is unused, and journal_sectors is zero.

Calculating the journal watermark requires dividing by journal_sectors,
which should be done only if the journal is configured.

Otherwise, a simple table query (dmsetup table) can cause OOPS.

This bug did not show on some systems, perhaps only due to
compiler optimization.

On my 32-bit testing machine, this reliably crashes with the following:

: Oops: divide error: 0000 [#1] PREEMPT SMP
: CPU: 0 UID: 0 PID: 2450 Comm: dmsetup Not tainted 6.14.0-rc2+ #959
: EIP: dm_integrity_status+0x2f8/0xab0 [dm_integrity]
...