net/sched: sch_hfsc: fix divide-by-zero in rtsc_min()

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SUSE CVE-2026-31423

In the Linux kernel, the following vulnerability has been resolved: net/sched: schhfsc: fix divide-by-zero in rtscmin m2sm converts a u32 slope to a u64 scaled value. For large inputs e.g. m1=4000000000, the result can reach 2^32. rtscmin stores the difference of two such u64 values in a u32...