LTDC modifies the clock frequency to adapt it to the display. Such
frequency change is not detected by the FDCAN driver that instead
caches the value at probe and pretends to use it later.

This change fixes the issue by moving the FDCAN to PLL4_R,
leaving the LTDC alone on PLL4_Q.

Signed-off-by: Antonio Borneo <antonio.borneo@st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I8230868b2b5fd6deb6e3f9dc3911030d8d484c58