iio:accel:adis16201: Fix wrong axis assignment that prevents loading

Whilst running some basic tests as part of writing up the dt-bindings for
this driver (to follow), it became clear it doesn't actually load
currently.

iio iio:device1: tried to double register : in_incli_x_index
adis16201 spi0.0: Failed to create buffer sysfs interfaces
adis16201: probe of spi0.0 failed with error -16

Looks like a cut and paste / update bug.  Fixes tag obviously not accurate
but we don't want to bother carry thing back to before the driver moved
out of staging.

Fixes: 591298e5 ("Staging: iio: accel: adis16201: Move adis16201 driver out of staging")
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: <Stable@vger.kernel.org>
Cc: Himanshu Jha <himanshujha199640@gmail.com>
Cc: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Alexandru Ardelean <ardeleanalex@gmail.com>
Link: https://lore.kernel.org/r/20210321182956.844652-1-jic23@kernel.org