Fix escaping of rhs for @atomic a.x = y

[tkf]

This PR fixes escaping of atomic setproperty! syntax @atomic a.x = y. Before this PR:

julia> mutable struct A
           @atomic x::Int
       end

julia> f!(a, y) = @atomic a.x = y;

julia> f!(A(0), 1)
ERROR: UndefVarError: y not defined

[vtjnash]

Thanks! Looks like I got all the other cases?

[tkf]

Yeah, I eyeballed other cases but couldn't find anything similar.