Staging: fix iio builds when IIO_RING_BUFFER is not enabled

Fix build by moving enum list outside of
#ifdef CONFIG_IIO_RING_BUFFER.

drivers/staging/iio/accel/adis16201_core.c:413: error: 'ADIS16201_SCAN_SUPPLY' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:417: error: 'ADIS16201_SCAN_TEMP' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:422: error: 'ADIS16201_SCAN_ACC_X' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:427: error: 'ADIS16201_SCAN_ACC_Y' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:432: error: 'ADIS16201_SCAN_AUX_ADC' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:436: error: 'ADIS16201_SCAN_INCLI_X' undeclared here (not in a function)
drivers/staging/iio/accel/adis16201_core.c:441: error: 'ADIS16201_SCAN_INCLI_Y' undeclared here (not in a function)

vers/staging/iio/accel/adis16203_core.c:374: error: 'ADIS16203_SCAN_SUPPLY' undeclared here (not in a function)
drivers/staging/iio/accel/adis16203_core.c:378: error: 'ADIS16203_SCAN_AUX_ADC' undeclared here (not in a function)
drivers/staging/iio/accel/adis16203_core.c:382: error: 'ADIS16203_SCAN_INCLI_X' undeclared here (not in a function)
drivers/staging/iio/accel/adis16203_core.c:388: error: 'ADIS16203_SCAN_INCLI_Y' undeclared here (not in a function)
drivers/staging/iio/accel/adis16203_core.c:392: error: 'ADIS16203_SCAN_TEMP' undeclared here (not in a function)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>