boards: st: nucleo_wb05kz: use STM32_CLOCK

This board was introduced concurrently with the STM32_CLOCK macro, so the
board's DTS uses the old method instead of the macro to specify clocks.

Update the DTS to use the STM32_CLOCK macro as other places do now.

Signed-off-by: Mathieu Choplain <mathieu.choplain@st.com>