[mlir][func] Fix incorrect API usage in `FuncOpConversion` (#113977)
This commit fixes a case of incorrect dialect conversion API usage
during `FuncOpConversion`. `replaceAllUsesExcept` (same as
`replaceAllUsesWith`) is currently not supported in a dialect
conversion. `replaceUsesOfBlockArgument` should be used instead. It
sometimes works anyway (like in this case), but that's just because of
the way we insert materializations.
This commit is in preparation of merging the 1:1 and 1:N dialect
conversion drivers. (At that point, the current use of
`replaceAllUsesExcept` will no longer work.)