I would no advise trying to weld it simply because of the cost of buying a replacement 2nd hand one (dependant on your location of course).
Most of the metals on these bikes aren't the most pure and hence it can be tricky to get a strong weld, but certainly not impossible. Bare in mind the bracket has to hold up the entire weight of a pillion and more when they stand on it to swing their right leg over.
Are you sure that the bracket is the piece that bent? Normally it is the mounting plate which is welded onto the frame that bends.
All the best,
Bullet5.