clk: clk-flexgen: fix clock-critical handling

clk: clk-flexgen: fix clock-critical handling

Fixes an issue leading to having all clocks following a critical
clocks marked as well as criticals.

Fixes: fa6415affe20 ("clk: st: clk-flexgen: Detect critical clocks")
Signed-off-by: Alain Volmat <avolmat@me.com>
Link: https://lkml.kernel.org/r/20200322140740.3970-1-avolmat@me.com
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>