fix(st-clock): remove useless switch

This corrects MISRA C2012-16.6:
Every switch statement shall have at least two switch-clauses.
While at it, remove useless rate variable.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I123784e7184dbf4146fd0d7faeffd6a0382fc6a1
1 file changed