bug: Let report_bug_entry() provide the correct bugaddr

bug: Let report_bug_entry() provide the correct bugaddr

report_bug_entry() always provides zero for bugaddr but could easily
extract the correct address from the provided bug_entry. Just do that to
have proper warning messages.

E.g. adding an artificial:

  void foo(void) { WARN_ONCE(1, "bar"); }

function generates this warning message:

  WARNING: arch/s390/kernel/setup.c:1017 at 0x0, CPU#0: swapper/0/0
                                            ^^^

With the correct bug address this changes to:

  WARNING: arch/s390/kernel/setup.c:1017 at foo+0x1c/0x40, CPU#0: swapper/0/0
                                            ^^^^^^^^^^^^^

Fixes: 7d2c27a0ec5e ("bug: Add report_bug_entry()")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://patch.msgid.link/20251208200658.3431511-1-hca@linux.ibm.com