iio: chemical: bme680_spi: remove bits_per_word = 8

Remove setting bits_per_word = 8 from the bme680 driver. This is the
default value for SPI transfers, so it is not necessary to explicitly
set it.

Since no other SPI settings are changed, we can also remove the call to
spi_setup().

Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250505-iio-remove-bits_per_word-8-v1-3-341f85fcfe11@baylibre.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>