Proving that a scheme is not IND-CPA-secure
Seems like you're getting confused between two different notations. Generally, in the experiment, adversary $A$ will output a bit $b'$. So, we have the following notations which refer to the bit $b'$ output by $A$:
$$Pr[A(n)=1]$$
and
$$Pr[A(n)=0]$$

Now, $A$ is said to have won the experiment if $b'=b$ and that is captured by the following notation. Here, we are interested in the outcome of the experiment. 
$$Pr[Game_A^{CPA}(n)=1]$$

The $=1$ in the above should not be confused with $A$'s output. Rather $1$ means $A$ wins (i.e. $b'=b$) and $0$ means $A$ loses (i.e. $b' \neq b$)