atmel_qspi objects are kept in spi_controller objects, so, first get
pointer to spi_controller object and then get atmel_qspi object from
spi_controller object.

Fixes: 2d30ac5e ("mtd: spi-nor: atmel-quadspi: Use spi-mem interface for atmel-quadspi driver")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Mark Brown <broonie@kernel.org>