cmd/compile: fix missing update source type in storeArgOrLoad

After removing trivial wrapper types, the source needs to be updated
with new type, otherwise, it leads to mismatch between field offset and
the source type for selecting struct/array.

Fixes #49249

Change-Id: I26f9440bcb2e78bcf0617afc21d9d40cdbe4aca6
Reviewed-on: https://go-review.googlesource.com/c/go/+/360057


Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>