Input: ads7846: do not overwrite spi->mode flags set by spi framework

Do not overwrite spi->mode flags set by spi framework, otherwise the
chip select polarity will get lost.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Link: https://lore.kernel.org/r/20201027095724.18654-3-o.rempel@pengutronix.de


Signed-off-by: Mark Brown <broonie@kernel.org>