drivers: clk: st: Fix FSYN channel values

This patch fixes the value for disabling the FSYN channel clock.
The 'is_enabled' returned value is also fixed.

Signed-off-by: Pankaj Dev <pankaj.dev@st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>