spi: f-ospi: Add missing spi_mem_default_supports_op() helper

The .supports_op() callback function returns true by default after
performing driver-specific checks. Therefore the driver cannot apply
the buswidth in devicetree.

Call spi_mem_default_supports_op() helper to handle the buswidth
in devicetree.

Fixes: 358f803a ("spi: Add Socionext F_OSPI SPI flash controller driver")
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>