spi: atmel-quadspi: Fix the buswidth adjustment between spi-mem and controller

Use the spi_mem_default_supports_op() core helper in order to take into
account the buswidth specified by the user in device tree.

Cc: <stable@vger.kernel.org>
Fixes: 0e6aae08

 ("spi: Add QuadSPI driver for Atmel SAMA5D2")
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20220406133604.455356-1-tudor.ambarus@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>