drivers: flash: stm32: qspi: remove flag_quad_io_en field
drivers: flash: stm32: qspi: remove flag_quad_io_en field

There is no need in the `flag_quad_io_en` field.
When QE enabling failed, then the driver `init` fails as well.

There is no way to use qspi in quad mode if qe is not enabled.

Signed-off-by: Georgij Cernysiov <bd22e7942bc8beaebb3a0cc77ee92e4585e26366@gmail.com>

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