Auto merge of #115595 - surechen:114896, r=davidtwco

Fix incorrect mutable suggestion information for binding in ref pattern like:  `let &b = a;`

fixes #114896

I find we have to get pat_span but not local_decl.source_info.span for suggestion. In `let &b = a;`  pat_span is &b. I think check `let &b = a` in hir to make sure it is hir::Node::Local(hir::Local {pat: hir::Pat{kind: hir::PatKind::Ref(.......   can distinguish it from other situation, but I'm not sure.

If my processing method is not accurate, please guide me to modify it, thank you.

r? `@davidtwco`

Author: bors