website: Update broken link in reporting_problems.md

Change-Id: Ib07592a79e78d779da3a87703f9883184e70c30e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/38875
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: Jason Lowe-Power <power.jg@gmail.com>
1 file changed