dts: arm: stm32u5 octospi clock source
dts: arm: stm32u5 octospi clock source

The definition of the clock source for the 2 octospi
instances is given by the DTS node.
The default value selects the sysclk (not pclk)
for the alternate clock control.

Signed-off-by: Francois Ramu <b83adc7f8a23ee911a37fcb61c4033581aae0b7a@st.com>

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