spi: atmel-quadspi: return appropriate error code

Return -ENOTSUPP when atmel_qspi_find_mode() fails. Propagate
the error in atmel_qspi_exec_op().

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed