drivers: flash: fix hyperflash write operations

Hyperflash write operations resulted in invalid writes. This commit
fixes the issue by temporarily lowering the clock during writes.
This aligns with the mcux-sdk-examples.

Fixes https://github.com/zephyrproject-rtos/zephyr/issues/53855



Signed-off-by: Jeppe Odgaard <jeppe.odgaard@prevas.dk>